# Big Ideas Math Geometry Answers Chapter 5 Congruent Triangles

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## Big Ideas Math Book Geometry Answer Key Chapter 5 Congruent Triangles

Prepare using the Big Ideas Math Book Geometry chapter 5 Congruent Triangles Answer Key and get a good hold of the entire concepts. Clarify all your doubts taking help of the BIM Book Geometry Ch 5 Congruent Triangles Solutions provided. Simply tap on the BIM Geometry Chapter 5 Congruent Triangles Answers and prepare the corresponding topic in no time. Big Ideas Math Geometry Congruent Triangles Solution Key covers questions from Lessons 5.1 to 5.8, Practice Tests, Assessment Tests, Chapter Tests, etc. Attempt the exam with confidence and score better grades in exams.

### Congruent Triangles Maintaining Mathematical Proficiency

Find the coordinates of the midpoint M of the segment with the given endpoints. Then find the distance between the two points.

Question 1.
P(- 4, 1) and Q(0, 7)
The given points are:
P (-4, 1), Q (0, 7)
We know that,
The midpoint M of the segment with the 2 endpoints is:
( $$\frac{x1 + x2}{2}$$, $$\frac{y1 + y2}{2}$$ )
Let the give points are:
(x1, y1) and (x2, y2)
So,
By comparing the given poits,
We will get
x1 = -4, x2 = 0, y1 = 1, y2 = 7
Hence,
The midpoint M = ( $$\frac{-4 + 0}{2}$$, $$\frac{1 + 7}{2}$$ )
= ( $$\frac{-4}{2}$$, $$\frac{8}{2}$$ )
= (-2, 4)
Hence, from the above,
We can conclude that the midpoint M of the segment with the given endpoints is: (-2, 4)

Question 2.
G(3, 6) and H(9, – 2)
The given points are:
G (3, 6), H (9, -2)
We know that,
The midpoint M of the segment with the 2 endpoints is:
( $$\frac{x1 + x2}{2}$$, $$\frac{y1 + y2}{2}$$ )
Let the give points are:
(x1, y1) and (x2, y2)
So,
By comparing the given poits,
We will get
x1 = 3, x2 = 9, y1 = 6, y2 = -2
Hence,
The midpoint M = ( $$\frac{3 + 9}{2}$$, $$\frac{6 – 2}{2}$$ )
= ( $$\frac{12}{2}$$, $$\frac{4}{2}$$ )
= (6, 2)
Hence, from the above,
We can conclude that the midpoint M of the segment with the given endpoints is: (6, 2)

Question 3.
U(- 1, – 2) and V(8, 0)
The given points are:
U (-1, -2), V (8, 0)
We know that,
The midpoint M of the segment with the 2 endpoints is:
( $$\frac{x1 + x2}{2}$$, $$\frac{y1 + y2}{2}$$ )
Let the give points are:
(x1, y1) and (x2, y2)
So,
By comparing the given poits,
We will get
x1 = -1, x2 = 8, y1 = -2, y2 = 0
Hence,
The midpoint M = ( $$\frac{-1 + 8}{2}$$, $$\frac{-2 + 0}{2}$$ )
= ( $$\frac{7}{2}$$, $$\frac{-2}{2}$$ )
= ( $$\frac{7}{2}$$, -1 )
Hence, from the above,
We can conclude that the midpoint M of the segment with the given endpoints is: ( $$\frac{7}{2}$$, -1 )

Solve the equation.

Question 4.
7x + 12 = 3x
The given equation is:
7x + 12 = 3x
So,
7x – 3x = 12
4x = 12
x = $$\frac{12}{4}$$
x = 3
Hence, from the above,
We can conclude that the value of x is: 3

Question 5.
14 – 6t = t
The given equation is:
14 – 6t = t
So,
14 = 6t + t
7t = 14
t = $$\frac{14}{7}$$
t = 2
Hence, from the above,
We can conclude that the value of t is: 2

Question 6.
5p + 10 = 8p + 1
The given equation is:
5p + 10 = 8p + 1
So,
5p – 8p = 1 – 10
-3p = -9
3p = 9
p = $$\frac{9}{3}$$
p = 3
Hence, from the above,
We can conclude that the value of p is: 3

Question 7.
w + 13 = 11w – 7
The given equation is:
w + 13 = 11w – 7
So,
w – 11w = -7 – 13
-10w = -20
10w = 20
w = $$\frac{20}{10}$$
w = 2
Hence, from the above,
We can conclude that the value of w is: 2

Question 8.
4x + 1 = 3 – 2x
The given equation is:
4x + 1 = 3 – 2x
So,
4x + 2x = 3 – 1
6x = 2
x = $$\frac{2}{6}$$
x = $$\frac{1}{3}$$
Hence, from the above,
We can conclude that the value of x is: $$\frac{1}{3}$$

Question 9.
z – 2 = 4 + 9z
The given equation is:
z – 2 = 4 + 9z
So,
z – 9z = 4 + 2
-8z = 6
z = –$$\frac{6}{8}$$
z = –$$\frac{3}{4}$$
Hence, from the above,
We can conclude that the value of z is: –$$\frac{3}{4}$$

Question 10.
ABSTRACT REASONING
Is it possible to find the length of a segment in a coordinate plane without using the Distance Formula? Explain your reasoning.
Yes, it is possible to find the length of a segment in a coordinate plane without using the distance formula
Since the segment is a portion of a line, we can use the graph to calculate the distance of a segment even though it would not provide accurate results.
Hence,
We use the distance formula to find the length of a segment in a coordinate plane

### Congruent Triangles Mathematical Practices

Monitoring Progress

Classify each statement as a definition, a postulate, or a theorem. Explain your reasoning.

Question 1.
In a coordinate plane, two non-vertical lines are perpendicular if and only if the product of their slopes is – 1.
The given statement is:
In a coordinate plane, two non-vertical lines are perpendicular if and only if the product of their slopes is – 1.
We know that,
According to the “parallel and perpendicular lines theorem”, two non-vertical lines are perpendicular if and only if the product of their slopes is -1
Hence, from the above,
We can conclude that the given statement is a Theorem

Question 2.
If two lines intersect to form a linear pair of congruent angles, then the lines are perpendicular.
The given statement is:
If two lines intersect to form a linear pair of congruent angles, then the lines are perpendicular.
We know that,
According to the “Linear pair perpendicular theorem”,
When two straight lines intersect at a point and form a linear pair of congruent angles, then the lines are perpendicular
Hence, from the above,
We can conclude that the given statement is a Theorem

Question 3.
If two lines intersect to form a right angle. then the lines are perpendicular.
The given statement is:
If two lines intersect to form a right angle. then the lines are perpendicular.
We know that,
According to the “Perpendicular lines theorem”,
When two lines intersect to form a right angle, the lines are perpendicular
Hence, from the above,
We can conclude that the given statement is a Theorem

Question 4.
Through any two points, there exists exactly one line.
The given statement is:
Through any two points, there exists exactly one line
We know that,
Between two points, only one line can be drawn and we don’t need any proof to prove the above statement
We know that,
The statement that is true without proof to prove is called “Postulate”
Hence, from the above,
We can conclude that the given statement is a Postulate

### 5.1 Angles of Triangles

Exploration 1

Writing a Conjecture

Work with a partner.

a. Use dynamic geometry software to draw any triangle and label it ∆ABC.
By using the dynamic geometry software, the triangle drawn is:

b. Find the measures of the interior angles of the triangle.
From part (a),
We can observe that the vertices of the triangle are: A, B, and C
Let the interior angles of the vertices A, B, and C be α, β, and γ respectively
Hence,
The measures of the given triangle are:

Hence, from the above,
The measures of the interior angles are:
α = 62.1°, β = 64.1°, and γ = 53.8°

c. Find the sum of the interior angle measures.
From part (b),
The measures of the interior angles are:
α = 62.1°, β = 64.1°, and γ = 53.8°
Hence,
The sum of the interior angles = 62.1° + 64.1° + 53.1° = 180°
Hence, from the above,
We can conclude that the sum of the interior angle measures is: 180°

d. Repeat parts (a)-(c) with several other triangles. Then write a conjecture about the sum of the measures of the interior angles of a triangle.
The representation of the 3 different triangles and their internal angle measures is:

Hence, from the above,
We can conclude that the conjecture about the sum of the measures of the interior angles of a triangle is:
The sum of the internal angle measures of a triangle is always: 180°

CONSTRUCTING VIABLE ARGUMENTS
To be proficient in math, you need to reason inductively about data and write conjectures.
Inductive reasoning:
Inductive reasoning is the process of arriving at a conclusion based on a set of observations.
Inductive reasoning is used in geometry in a similar way.
Conjecture:
A statement you believe to be true based on inductive reasoning.

Exploration 2

Writing a Conjecture

Work With a partner.

a. Use dynamic geometry software to draw any triangle and label it ∆ABC.
The triangle drawn by using the dynamic geometry software is:

Hence, from the above,
We can conclude that the vertices of the triangle are: A, B, and C

b. Draw an exterior angle at any vertex and find its measure.
From part (a),
The vertices of the triangle are: A, B, and C
Let the external angle measures of the triangle are: α, β, and γ
Hence,
The representation of the external angle measures of the triangle are:

Hence,
From the above,
We can conclude that
The external angle measures of the triangle are:
α = 310.7°, β = 299.3°, and γ = 290°

c. Find the measures of the two nonadjacent interior angles of the triangle.
From part (b),
The external angle measures of the triangle are:
α = 310.7°, β = 299.3°, and γ = 290°
Hence,
The representation of the non-adjacent interior angles and the external angle measures of the triangle are:

Hence, from the above,
The angle measures of two non-adjacent sides are:
α = 70°, β = 60.7°, and γ = 49.3°

d. Find the sum of the measures of the two nonadjacent interior angles. Compare this sum to the measure of the exterior angle.
From part (b),
The external angle measures of the triangle are:
α = 310.7°, β = 299.3°, and γ = 290°
From part (c),
The measures of the two non-adjacent interior angles are:
α = 70°, β = 60.7°, and γ = 49.3°
Now,
The sum of the measures of the external angles of the triangle are:
α + β + γ = 310.7° + 299.3°+ 290°
= 900.0°
The sum of the measures of the two non-adjacent interior angles is:
α + β + γ = 70° + 60.7° + 49.3°
= 180.0
Hence, from the above,
We can conclude that the sum of the measures of the external angles is 5 times the sum of the measures of the two non-adjacent interior angles

e. Repeat parts (a)-(d) with several other triangles. Then write a conjecture that compares the measure of an exterior angle with the sum of the measures of the two nonadjacent interior angles.

Hence, from the above,
We can conclude that
The external angle measure of a vertex for a given triangle = 360° – (Internal angle measure of a vertex that we are finding the external angle measure)
The sum of the internal angle measures of the triangle is: 180°

Question 3.
How are the angle measures of a triangle related?
The angle measures of a triangle are related as shown below:
The external angle measure of a vertex for a given triangle = 360° – (Internal angle measure of a vertex that we are finding the external angle measure)
The sum of the internal angle measures of the triangle is: 180°

Question 4.
An exterior angle of a triangle measures 32° What do you know about the measures of the interior angles? Explain your reasoning.
It is given that an exterior angle of a triangle measures 32°
We know that,
The external angle measure of a vertex for a given triangle = 360° – (Internal angle measure of a vertex that we are finding the external angle measure)
So,
32° = 360° – (The internal angle measure of 32°)
The internal angle measure of 32° = 360° – 32°
The interior angle measure of 32° = 328°
Hence, from the above,
We can conclude that the interior angle measure of a triangle for an external angle measure of 32° is: 328°

### Lesson 5.1 Angles of Triangles

Monitoring Progress

Question 1.
Draw an obtuse isosceles triangle and an acute scalene triangle.
The figures of an obtuse isosceles triangle and an acute triangle are as follows:

Question 2.
∆ABC has vertices A(0, 0), B(3, 3), and C(- 3, 3), Classify the triangle by its sides. Then determine whether it is a right triangle.
The given points are:
A (0, 0), B (3, 3), and C (-3, 3)
and the triangle is ΔABC
We know that,
To find whether the given triangle is a right-angled triangle or not,
We have to prove,
AC² = AB² + BC²
Where,
AC is the distance between A and C points
AB is the distance between A and B points
BC is the distance between B and C points
We know that,
The distance between 2 points = √(x2 – x1)² + (y2 – y1)²
Now,
Let the given points be considered as A(x1, y1), B(x2, y2), and C( x3, y3)
So,
AB = √(3 – 0)² + (3 – 0)² = √3² + 3²
= √9 + 9 = √18
BC = √(-3 – 3)² + (3 – 3)²
= √(-6)² + 0²
= √6² = 6
AC = √(-3 – 0)² + (3 – 0)²
= √(-3)² + 3²
= √9 + 9 = √18
Now,
AC² = AB² + BC²
(√18)² = (√18)² + 6²
18 = 18 + 36
18 ≠54
Hence, from the above,
We can conclude that the given triangle is not a right-angled triangle

Question 3.
Find the measure of ∠1

The given figure is:

We know that,
The measure of an exterior angle of a triangle is equal to the sum of the measures of the two non-adjacent interior angles
From the given triangle,
The exterior angle is: (5x – 10)°
The interior angles are: 40°, 3x°, ∠1
So,
(5x – 10)° = 40° + 3x°
5x° – 3x° = 40° + 10°
2x° = 50°
x = 50° ÷ 2
x = 25°
So,
The interior angles are 40°, 3 (25)°, ∠1
= 40°, 75°, ∠1
We know that,
The sum of the interior angles of a triangle is: 180°
So,
40° + 75° + ∠1 = 180°
115° + ∠1 = 180°
∠1 = 180° – 115°
∠1 = 65°
Hence, from the above,
We can conclude that the value of ∠1 is: 65°

Question 4.
Find the measure of each acute angle.

The given figure is:

We know that,
The sum of the interior angles in a triangle is: 180°
From the given figure,
The interior angles of the right-angled triangle are: 90°, 2x°, and (x – 6)°
So,
90° + 2x° + (x – 6)° = 180°
84°+ 3x° = 180°
3x° = 180° – 84°
3x° = 96°
x = 96° ÷ 3°
x = 32°
So,
The measure of each acute angle is 90°, 2x°, (x – 6)°
= 90°, 2(32)°, (32 – 6)°
= 90°, 64°, 26°
Hence, from the above,
We can conclude that,
The measure of each acute angle is 90°, 64°, and 26°

### Exercise 5.1 Angles of Triangles

Vocabulary and Core Concept Check

Question 1.
WRITING
Can a right triangle also be obtuse? Explain our reasoning.

Question 2.
COMPLETE THE SENTENCE
The measure of an exterior angle of a triangle is equal to the sum of the measures of the two ____________ interior angles.
The given statement is:
The measure of an exterior angle of a triangle is equal to the sum of the measures of the two ____________ interior angles.
Hence,
The completed form of the given statement is:
The measure of an exterior angle of a triangle is equal to the sum of the measures of the two non-adjacent interior angles.

Monitoring Progress and Modeling with Mathematics

In Exercises 3-6, classify the triangle by its sides and by measuring its angles.

Question 3.

Question 4.

The given figure is:

We know that,
“|” represents the “Congruent” or “Equal” in geometry
So,
From the given figure,
We can observe that all three sides of the given triangle are equal
We know that,
If a triangle has all the sides equal, then the triangle is called an “Equilateral triangle”
Hence, from the above,
We can conclude that the ΔLMN is an “Equilateral triangle”

Question 5.

Question 6.

The given figure is:

We know that,
If any side is not equal to each other in the triangle, then the triangle is called a “Scalene triangle”
The angle greater than 90° is called as “Obtuse angle”
An angle less than 90° is called an “Acute angle”
Hence, from the above,
We can conclude that ΔABC is an “Acute scalene triangle”

In Exercises 7-10, classify ∆ABC by its sides. Then determine whether it is a right triangle.

Question 7.
A(2, 3), B(6, 3), (2, 7)

Question 8.
A(3, 3), B(6, 9), (6, – 3)
The given points are:
A (3, 3), B(6, 9), and C (6, -3)
We know that,
To find whether the given triangle is a right angle or not,
We have to prove,
AC² = AB² + BC²
Where,
AC is the distance between points A and C
AB is the distance between points A and B
BC is the distance between points B and C
The slope of any one side must be equal to -1
Now,
Let the given points be
A (x1, y1), B(x2, y2), and C (x3, y3)
So,
A (x1, y1)= (3, 3), B (x2, y2) = (6, 9), and C (x3, y3) = (6, -3)
We know that,
The distance between 2 points = √(x2 – x1)² + (y2 – y1)²
So,
AB = √(6 – 3)² + (9 – 3)²
= √3² + 6²
= √9 + 36 = √45
BC = √6 – 6)² + (-3 – 9)²
= √0 + 12²
= √12² = 12
AC = √(6 – 3)² + (-3 – 3)²
= √(3)² + (-6)²
= √9 + 36 = √45
So,
From the length of the sides,
We can say that the given triangle is an Isosceles triangle,
We know that,
Slope (m) = $$\frac{y2 – y1} {x2 – x1}$$
So,
Slope of AB = $$\frac{9 – 3} {6 – 3}$$
= $$\frac{6} {3}$$
= 2
Slope of BC = $$\frac{-9 – 3} {6 – 6}$$
= $$\frac{-12} {0}$$
= Undefined
Slope of AC = $$\frac{-3 – 3} {6 – 3}$$
= $$\frac{-6} {3}$$
= -2
Hence, from the above,
We can conclude that the given triangle is not a right triangle

Question 9.
A(1, 9), B(4, 8), C(2, 5)

Question 10.
A(- 2, 3), B(0, – 3), C(3, – 2)
The given points are:
A (-2, 3), B(0, -3), and C (3, -2)
We know that,
To find whether the given triangle is a right angle or not,
We have to prove,
AC² = AB² + BC²
Where,
AC is the distance between points A and C
AB is the distance between points A and B
BC is the distance between points B and C
The slope of any one side must be equal to -1
Now,
Let the given points be
A (x1, y1), B(x2, y2), and C (x3, y3)
So,
A (x1, y1)= (-2, 3), B (x2, y2) = (0, -3), and C (x3, y3) = (3, -2)
We know that,
The distance between 2 points = √(x2 – x1)² + (y2 – y1)²
So,
AB = √(0 – [-2])² + (3 – 3)²
= √2² + 0²
= √4 + 0 = 2
BC = √3 – 0)² + (-2 -[-3] )²
= √9 + 1²
= √10
AC = √(3 – [-2])² + (-2 – 3)²
= √(5)² + (-5)²
= √25 + 25 = √50
Now,
AC² = AB² + BC²
50 = 10 + 4
50 ≠ 14
So,
From the length of the sides,
We can say that the given triangle is a scalene triangle since all the lengths of the sides are different
We know that,
Slope (m) = $$\frac{y2 – y1} {x2 – x1}$$
So,
Slope of AB = $$\frac{9 – 3} {6 – 3}$$
= $$\frac{6} {3}$$
= 2
Slope of BC = $$\frac{-9 – 3} {6 – 6}$$
= $$\frac{-12} {0}$$
= Undefined
Slope of AC = $$\frac{-3 – 3} {6 – 3}$$
= $$\frac{-6} {3}$$
= -2
Hence, from the above,
We can conclude that the given triangle is not a right triangle

In Exercises 11 – 14. find m∠1. Then classify the triangle by its angles

Question 11.

Question 12.

The given figure is:

We know that,
The sum of interior angles in a triangle is: 180°
So,
From the above,
The interior angles of the given triangle are: 40°,  30°,  ∠1
Now,
40° + 30° + ∠1 = 180°
70 + ∠1 = 180°
∠1 = 180° – 70°
∠1 = 110°
We know that,
The angle greater than 90° is called an “Obtuse angle”
Hence, from the above,
We can conclude that the given triangle is an “Obtuse angled triangle”

Question 13.

Question 14.

The given figure is:

We know that,
The sum of interior angles in a triangle is: 180°
So,
From the above,
The interior angles of the given triangle are: 60°,  60°,  ∠1
Now,
60° + 60° + ∠1 = 180°
120 + ∠1 = 180°
∠1 = 180° – 120°
∠1 = 60°
We know that,
An angle less than 90° is called an “Acute angle”
The triangle that all the angles 60° is called an “Equilateral triangle”
Hence, from the above,
We can conclude that the given triangle is an “Equilateral triangle”

In Exercises 15-18, find the measure of the exterior angle.

Question 15.

Question 16.

The given figure is:

We know that,
An exterior angle is equal to the sum of the two non-adjacent interior angles in a triangle
So,
(2x – 2)° = x° + 45°
2x° – x° = 45° + 2°
x = 47°
Hence,
The measure of the exterior angle is: (2x – 2)°
= (2 (47) – 2)°
= (94 – 2)°
= 92°
Hence, from the above,
We can conclude that the measure of the exterior angle is: 92°

Question 17.

Question 18.

The given figure is:

We know that,
An exterior angle is equal to the sum of the two non-adjacent interior angles in a triangle
So,
(7x – 16)° = (x + 8)° + 4x°
7x° – 5x° = 16° + 8°
2x = 24°
x = 24° ÷ 2
x = 12°
Hence,
The measure of the exterior angle is: (7x – 16)°
= (7 (12) – 16)°
= (84 – 16)°
= 68°
Hence, from the above,
We can conclude that the measure of the exterior angle is: 68°

In Exercises 19-22, find the measure of each acute angle.

Question 19.

Question 20.

The given figure is:

From the given figure,
We can observe that one angle is 90° and the 2 sides are perpendicular
So,
We can say that the given triangle is a right-angled triangle
We know that,
The sum of interior angles of a triangle is: 180°
So,
x° + (3x + 2)° + 90° = 180°
4x° + 2° + 90° = 180°
4x° = 180° – 90° – 2°
4x° = 88°
x = 88° ÷ 4°
x = 22°
So,
The 2 acute angle measures are: x° and (3x + 2)°
= 22° and (3(22) + 2)°
= 22° and (66 + 2)°
= 22° and 68°
Hence, from the above,
We can conclude that the 2 acute angle measures are: 22° and 68°

Question 21.

Question 22.

The given figure is:

From the given figure,
We can observe that one angle is 90° and the 2 sides are perpendicular
So,
We can say that the given triangle is a right-angled triangle
We know that,
The sum of interior angles of a triangle is: 180°
So,
(19x – 1)° + (13x – 5)° + 90° = 180°
32x° – 6° + 90° = 180°
32x° = 180° – 90° – 6°
4x° = 84°
x = 84° ÷ 4°
x = 21°
So,
The 2 acute angle measures are: (19x – 1)° and (13x – 5)°
= (19 (21) – 1)° and (13(21) – 5)°
= 398° and (273 – 5)°
= 398° and 268°
Hence, from the above,
We can conclude that the 2 acute angle measures are: 398° and 268°

In Exercises 23-26. find the measure of each acute angle in the right triangle.

Question 23.
The measure of one acute angle is 5 times the measure of the other acute angle.

Question 24.
The measure of one acute angle is times the measure of the other acute angle.

Question 25.
The measure of one acute angle is 3 times the sum of the measure of the other acute angle and 8.

Question 26.
The measure of one acute angle is twice the difference of the measure of the other acute angle and 12.
The given statement is:
The measure of one acute angle is twice the difference of the measure of the other acute angle and 12.
So,
x° + [2 (x – 12)]° = 90°
x° + 2x° – 2(12)° = 90°
3x° – 24° = 90°
3x° = 90° + 24°
3x° = 114°
x = 114° ÷ 3
x = 38°
So,
The 2 acute angle measures are: x°, 2 (x – 12)°
= 38°, 2 (38 – 12)°
= 38°, 2(26)°
= 38° , 52°
Hence, from the above,
We can conclude that the acute angle measures are: 38°, 52°

ERROR ANALYSIS
In Exercises 27 and 28, describe and correct the error in finding m∠1.

Question 27.

Question 28.

We know that,
The exterior angle of a triangle is equal to the sum of the non-adjacent interior angles of a triangle
So,
From the figure,
The external angle is: ∠1
The interior angles are 80°, 50°
So,
∠1 = 80° + 50°
∠1 = 130°
Now,
The interior angle measure of ∠1= 180° – (External angle measure of 130°)
= 180° – 130°
= 50°
Hence, from the above,
The internal angle measure of ∠1 is: 50°

In Exercises 29-36, find the measure of the numbered angle.

Question 29.
∠1

Question 30.
∠2
We know that,
The external angle measure is equal to the sum of the non-adjacent interior angles
So,
∠2 = 90° + 40°
∠2 = 130°

Question 31.
∠3

Question 32.
∠3
From the above figure,
∠2 = ∠4
Hence, from the above,
We can conclude that
∠2 = ∠4 = 130°

Question 33.
∠5

Question 34.
∠6
The external angle measure is equal to the sum of the non-adjacent interior angles
So,
∠6 = 90° + ∠3
∠6 = 90° + 50°
∠6 = 140°

Question 35.
∠7

Question 36.
∠8
The external angle measure is equal to the sum of the non-adjacent interior angles
So,
∠8 = 90° + ∠1
∠6 = 90° + 50°
∠6 = 140°

Question 37.
USING TOOLS
Three people are standing on a stage. The distances between the three people are shown in the diagram. Classify the triangle by its sides and by measuring its angles.

Question 38.
USING STRUCTURE
Which of the following sets of angle measures could form a triangle? Select all that apply.
(A) 100°, 50°, 40°
The given angles are: 100°, 50°, 40°
We know that,
The sum of the angles of a triangle should be equal to 180°
So,
The sum of the given angles = 100° + 50° + 40°
= 100° + 90°
= 190°
Hence, from the above,
We can conclude that the given angles do not form a triangle

(B) 96°, 74°, 10°
The given angles are: 96°, 74°, 10°
We know that,
The sum of the angles of a triangle should be equal to 180°
So,
The sum of the given angles = 96° + 74° + 10°
= 96° + 84°
= 180°
Hence, from the above,
We can conclude that the given angles forms a triangle

(C) 165°, 113°, 82°
The given angles are: 165°, 113°, 82°
We know that,
The sum of the angles of a triangle should be equal to 180°
So,
The sum of the given angles = 165° + 113° + 82°
= 165° + 195°
= 360°
But,
We know that,
The sum of exterior angles of a triangle is: 360°
Hence, from the above,
We can conclude that the given angles forms a triangle

(D) 101°, 41°, 38°
The given angles are: 101°, 41°, 38°
We know that,
The sum of the angles of a triangle should be equal to 180°
So,
The sum of the given angles = 101° + 38° + 41°
= 101° + 79°
= 180°
Hence, from the above,
We can conclude that the given angles forms a triangle

(E) 90°, 45°, 45°
The given angles are: 90°, 45°, 45°
We know that,
The sum of the angles of a triangle should be equal to 180°
So,
The sum of the given angles = 90° + 45° + 45°
= 90° + 90°
= 180°
Hence, from the above,
We can conclude that the given angles forms a triangle

(F) 84°, 62°, 34°
The given angles are: 84°, 62°, 34°
We know that,
The sum of the angles of a triangle should be equal to 180°
So,
The sum of the given angles = 84° + 62° + 34°
= 84° + 96°
= 180°
Hence, from the above,
We can conclude that the given angles forms a triangle

Question 39.
MODELING WITH MATHEMATICS
You are bending a strip of metal into an isosceles triangle for a sculpture. The strip of metal is 20 inches long. The first bend is made 6 inches from one end. Describe two ways you could complete the triangle.

Question 40.
THOUGHT-PROVOKING
Find and draw an object (or part of an object) that can be modeled by a triangle and an exterior angle. Describe the relationship between the interior angles of the triangle and the exterior angle in terms of the object.

From the above figure,
We can say that
The sum of the interior angles of a given triangle is: 180°
The sum of the exterior angles of a given triangle is: 360°
The relation between the interior angles and the exterior angles is:
The exterior angle measure = Sum of the two non-adjacent interior angles

Question 41.
PROVING A COROLLARY
Prove the Corollary to the Triangle Sum Theorem (Corollary 5. 1).
Given ∆ABC is a right triangle
Prove ∠A and ∠B are complementary

Question 42.
PROVING A THEOREM
Prove the Exterior Angle Theorem (Theorem 5.2).
Given ∆ABC, exterior ∠ACD
Prove m∠A + m∠B = m∠ACD

It is given that
In ΔABC, the exterior angle is ∠ACD
We have to prove that
m∠A + m∠B = m∠ACD
Proof:

Hence, from the above,
We can conclude that
m∠A + m∠B = m∠ACD is proven

Question 43.
CRITICAL THINKING
Is it possible to draw an obtuse isosceles triangle? obtuse equilateral triangle? If so, provide examples. If not, explain why it is not possible.

Question 44.
CRITICAL THINKING
Is it possible to draw a right isosceles triangle? right equilateral triangle? If so, provide an example. If not, explain why it is not possible.
It is possible to draw a right isosceles triangle but it is not possible to draw a right equilateral triangle
We know that,
In a triangle, if the length of the 2 sides are equal and one angle is a right-angle, then, it is called an “Right Isosceles triangle”
In a triangle, if the length of all the sides are equal and each angle is 60°, then it is an “Equilateral triangle”
Hence,
From the above definitions,
We can observe that it is possible to draw right isosceles triangle but it is not possible to dran a right equilateral triangle

Question 45.
MATHEMATICAL CONNECTIONS
∆ABC is isosceles.
AB = x, and BC = 2x – 4.
a. Find two possible values for x when the perimeter of ∆ABC is 32.
b. How many possible values are there for x when the perimeter of ∆ABC is 12?

Question 46.
HOW DO YOU SEE IT?
Classify the triangles, in as many ways as possible. without finding any measurements.
a.
The given figure is:

From the figure,
We can observe that all the length of the sides of the triangle are equal
We know that,
The triangle that has the length of all the sides equal is called an “Equilateral triangle”
Hence, from the above,
We can conclude that the given triangle is an “Equilateral triangle”

b.
The given figure is:

From the figure,
We can observe that the lengths of all the 3 sides are different
We know that,
The triangle that has all the different side lengths is called a “Scalene triangle”
Hence, from the above,
We can conclude that the given triangle is called a “Scalene triangle”

c.
The given figure is:

From the figure,
We can observe that the length of all the 3 sides are different and 1 angle is obtuse i.e., greater than 90°
We know that,
The triangle that has any angle obtuse is called an “Obtuse angled triangle”
Hence, from the above,
We can conclude that the given triangle is an “Obtuse angled scalene triangle”

d.
The given figure is:

From the figure,
We can observe that 1 angle is 90° and the 2 sides are perpendicular to each other
We know that,
The triangle that has an angle of 90° and the slope -1 is called a “Right-angled triangle”
Hence, from the above,
We can conclude that the given triangle is called a “Right-angled triangle”

Question 47.
ANALYZING RELATIONSHIPS
Which of the following could represent the measures of an exterior angle and two interior angles of a triangle? Select all that apply.
A) 100°, 62°, 38°
(B) 81°, 57°, 24°
(C) 119°, 68°, 49°
(D) 95°, 85°, 28°
(E) 92°, 78°, 68°
(F) 149°, 101°, 48°

Question 48.
MAKING AN ARGUMENT
Your friend claims the measure of an exterior angle will always be greater than the sum of the nonadjacent interior angle measures. Is your friend correct? Explain your reasoning.
No, your friend is not correct

Explanation:
We know that,
According to the exterior angle theorem,
The external angle measure is always equal to the sum of the non-adjacent internal angle measures
But,
The external angle measure will always be greater than the sum of the non-adjacent interior angle measures
Hence, from the above,
We can conclude that your friend is not correct

MATHEMATICAL CONNECTIONS
In Exercises 49-52, find the values of x and y.

Question 49.

Question 50.

The given figure is:

From the figure,
We have to obtain the values of x and y
Now,
By using the alternate angles theorem,
x = 118°
Now,
By using the exterior angle theorem,
x = y + 22°
y = x – 22°
y = 118° – 22°
y = 96°
Hence, from the above,
We can conclude that the values of x and y are: 118° and 96° respectively

Question 51.

Question 52.

The given figure is:

From the above figure,
We have to find the values of x and y
Now,
By using the sum of interior angle measures,
x° + 64° + 90° = 180°
x° + 154° = 180°
x° = 180° – 154°
x° = 26°
Now,
By using the exterior angle theorem,
y° = x° + 64°
y° = 26° + 64°
y° = 90°
Hence, from the above,
We can conclude that the values of x and y are: 26° and 90° respectively

Question 53.
PROVING A THEOREM
Use the diagram to write a proof of the Triangle Sum Theorem (Theorem 5. 1). Your proof should be different from the proof of the Triangle Sum Theorem shown in this lesson.

Maintaining Mathematical Proficiency

Use the diagram to find the measure of the segment or angle.

Question 54.
m∠KHL
From the given figures,
We can observe that
∠ABC = ∠GHK
∠KHL = ∠GHK / 2
So,
(6x + 2)° = (3x + 1)° + (5x – 27)°
6x – 3x – 5x = 1 – 27 – 2
6x – 8x = -27 – 1
-2x = -28
2x = 28
x = 28 ÷ 2
x = 14
So,
∠KHL = ∠GHK / 2
= [(3 (14) + 1)° + (5 (14) – 27)°] / 2
= [43° + 43°] / 2
= 86° / 2
= 43°
Hence, from the above,
We can conclude that
∠KHL = 43°

Question 55.
m∠ABC

Question 56.
GH
From the given figures,
We can observe that
AB = GH
So,
3y = 5y – 8
3y – 5y = -8
-2y = -8
2y = 8
y = 8 ÷ 2
y = 4
So,
The value of GH = 3y = 3 (4) = 12
Hence, from the above,
We can conclude that the value of GH is: 12

Question 57.
BC

### 5.2 Congruent Polygons

Exploration 1

Describing Rigid Motions

Work with a partner: of the four transformations you studied in Chapter 4, which are rigid motions? Under a rigid motion. why is the image of a triangle always congruent to the original triangle? Explain your reasoning.

Rigid motion occurs in geometry when an object moves but maintains its shape and size, which is unlike non-rigid motions, such as dilations, in which the object’s size changes. All rigid motion starts with the original object, called the pre-image, and results in the transformed object, called the image.
There are 4 types of rigid motion. They are:
a. Translation
b. Rotation
c. Reflection
d. Glide reflection
We know that,
Rotation only occurs in terms of 90° or 180°
Now,
The given transformations are:

So,
From the above figure,
The first figure and the second figure are different
The second figure and the third figure are the same in shape
The first figure and the fourth figure are the same in shape
So,
We can say that the first and the fourth figures are rigid motions
W can say that the second and the third figures are rigid motions
In the second and the third figures,
The “Rotation” takes place i.e., the second figure is rotated 180° keeping the original shape
In the first and the fourth figures,
The “Reflection” takes place i.e., the first figure is reflected keeping the original shape
Now,
The image of the triangle is always congruent to the original triangle because of the “Translation” i.e., the original triangle and the image of the triangle have the same sides and the same angles but not in the same position.

Exploration 2

Finding a Composition of Rigid Motions

Work with a partner. Describe a composition of rigid motions that maps ∆ABC to ∆DEF. Use dynamic geometry software to verify your answer.
LOOKING FOR STRUCTURE
To be proficient in math, you need to look closely to discern a pattern or structure.

a. ∆ABC ≅ ∆DEF

b. ∆ABC ≅ ∆DEF

c. ∆ABC ≅ ∆DEF

d. ∆ABC ≅ ∆DEF

Question 3.
Given two congruent triangles. how can you use rigid motions to map one triangle to the other triangle?

Question 4.
The vertices of ∆ABC are A(1, 1), B(3, 2), and C(4, 4). The vertices of ∆DEF are D(2, – 1), E(0, 0), and F(- 1, 2). Describe a composition of rigid motions that maps ∆ABC to ∆DEF.

### Lesson 5.2 Congruent Polygons

Monitoring Progress

In the diagram, ABGH ≅ CDEF.

Question 1.
Identify all pairs of congruent corresponding parts.

Question 2.
Find the value of x.

Question 3.
In the diagram at the left. show that ∆PTS ≅ ∆RTQ.

Use the diagram.

Question 4.
Find m∠DCN.

Question 5.
What additional information is needed to conclude that ∆NDC ≅ ∆NSR?

### Exercise 5.2 Congruent Polygons

Question 1.
WRITING
Based on this lesson. what information do you need to prove that two triangles are congruent? Explain your reasoning.

Question 2.
DIFFERENT WORDS, SAME QUESTION
Which is different? Find “both” answers.

Is ∆ABC ≅ ∆RST?

Is ∆KJL ≅ ∆SRT?

Is ∆JLK ≅ ∆STR?

Is ∆LKJ ≅ ∆TSR?

Monitoring Progress and Modeling with Mathematics

In Exercises 3 and 4. identify all pairs of congruent corresponding parts. Then write another congruence statement for the polygons.

Question 3.
∆ABC ≅ ∆DEF

Question 4.
GHJK ≅ ∆QRST

In Exercises 5-8, ∆XYZ ≅ ∆MNL. Copy and complete the statement.

Question 5.
m∠Y = ______

Question 6.
m∠M = ______

Question 7.
m∠Z = _______

Question 8.
XY= _______

In Exercises 9 and 10. find the values of x and y.

Question 9.
ABCD ≅ EFGH

Question 10.
∆MNP ≅ ∆TUS

In Exercises 11 and 12. show that the polygons are congruent. Explain your reasoning.

Question 11.

Question 12.

In Exercises 13 and 14, find m∠1.

Question 13.

Question 14.

Question 15.
PROOF
Triangular postage stamps, like the ones shown, are highly valued by stamp collectors. Prove that ∆AEB ≅ ∆CED.

Given $$\overline{A B}$$ || $$\overline{D C}$$, $$\overline{A B}$$ ≅ $$\overline{D C}$$ is the midpoint of $$\overline{A C}$$ and $$\overline{B D}$$
Prove ∆AEB ≅ ∆CED

Question 16.
PROOF
Use the information in the figure to prove that ∆ABG ≅ ∆DCF

ERROR ANALYSIS
In Exercises 17 and 18, describe and correct the error.

Question 17.

Question 18.

Question 19.
PROVING A THEOREM
Prove the Third Angles Theorem (Theorem 5.4) by using the Triangle Sum Theorem (Theorem 5. 1).

Question 20.
THOUGHT PROVOKING
Draw a triangle. Copy the triangle multiple times to create a rug design made of congruent triangles. Which property guarantees that all the triangles are congruent?

Question 21.
REASONING
∆JKL is congruent to ∆XYZ Identify all pairs of congruent corresponding parts.

Question 22.
HOW DO YOU SEE IT?
In the diagram, ABEF ≅ CDEF

a. Explain how you know that $$\overline{B E}$$ ≅ $$\overline{D E}$$ and ∠ABE ≅∠CDE.

b. Explain how you know that ∠GBE ≅ ∠GDE.

c. Explain how you know that ∠GEB ≅ ∠GED.

d. Do you have enough information to prove that ∠BEG ≅ ∠DEG? Explain.

MATHEMATICAL CONNECTIONS
In Exercises 23 and 24, use the given information to write and solve a system of linear equations to find the values of x and y.

Question 23.
∆LMN ≅ ∆PQR. m∠L = 40°, m∠M = 90° m∠P = (17x – y)°. m∠R (2x + 4y)°

Question 24.
∆STL ≅ ∆XYZ, m∠T = 28°, m∠U = (4x + y)°, m∠X = 130°, m∠Y = (8x – 6y)°

Question 25.
PROOF
Prove that the criteria for congruent triangles in this lesson is equivalent to the definition of congruence in terms of rigid motions.

Maintaining Mathematical Proficiency

What can you conclude from the diagram?

Question 26.

Question 27.

Question 28.

Question 29.

### 5.3 Proving Triangle Congruence by SAS

Exploration 1

Drawing Triangles

Work with a partner.

Use dynamic geometry software.
a. Construct circles with radii of 2 units and 3 units centered at the origin. Construct a 40° angle with its vertex at the origin. Label the vertex A.

b. Locate the point where one ray of the angle intersects the smaller circle and label this point B. Locate the point where the other ray of the angle intersects the larger circle and label this point C. Then draw ∆ABC.

c. Find BC, m∠B, and m∠C.

d. Repeat parts (a)-(c) several times. redrawing the angle indifferent positions. Keep track of your results by copying and completing the table below. What can you conclude?
USING TOOLS STRATEGICALLY
To be proficient in math, you need to use technology to help visualize the results of varying assumptions, explore consequences, and compare predictions with data.

Question 2.
What can you conclude about two triangles when you know that two pairs of corresponding sides and the corresponding included angles are congruent?

Question 3.
How would you prove your conclusion in Exploration 1(d)?

### Lesson 5.3 Proving Triangle Congruence by SAS

Monitoring Progress

In the diagram, ABCD is a square with four congruent sides and four right
angles. R, S, T, and U are the midpoints of the sides of ABCD. Also, $$\overline{R T}$$ ⊥ $$\overline{S U}$$ and $$\overline{S V}$$ ≅ $$\overline{V U}$$.

Question 1.
Prove that ∆SVR ≅ ∆UVR.

Question 2.
Prove that ∆BSR ≅ ∆DUT.

Question 3.
You are designing the window shown in the photo. You want to make ∆DRA congruent to ∆DRG. You design the window so that $$\overline{D A}$$ ≅ $$\overline{D G}$$ and ∠ADR ≅ ∠GDR. Use the SAS Congruence Theorem to prove ∆DRA ≅ ∆DRG.

### Exercise 5.3 Proving Triangle Congruence by SAS

vocabulary and core concept check

Question 1.
WRITING
What is an included angle?

Question 2.
COMPLETE THE SENTENCE
If two sides and the included angle of one triangle are congruent to two sides and the included angle of a second triangle, then __________ .

Monitoring progress and Modeling with Mathematics

In Exercises 3-8, name the included an1e between the pair of sides given.

Question 3.
$$\overline{J K}$$ and $$\overline{K L}$$

Question 4.
$$\overline{P K}$$ and $$\overline{L K}$$

Question 5.
$$\overline{L P}$$ and $$\overline{L K}$$

Question 6.
$$\overline{J L}$$ and $$\overline{J K}$$

Question 7.
$$\overline{K L}$$ and $$\overline{J L}$$

Question 8.
$$\overline{K P}$$ and $$\overline{P L}$$

In Exercises 9-14, decide whether enough information is given to prove that the triangles are congruent using the SAS Congruence Theorem (Theorem 5.5). Explain.

Question 9.
∆ABD, ∆CDB

Question 10.
∆LMN, ∆NQP

Question 11.
∆YXZ, ∆WXZ

Question 12.
∆QRV, ∆TSU

Question 13.
∆EFH, ∆GHF

Question 14.
∆KLM, ∆MNK

In Exercises 15 – 18, write a proof.

Question 15.
Given $$\overline{P Q}$$ bisects ∠SPT, $$\overline{S P}$$ ≅ $$\overline{T P}$$
Prove ∆SPQ ≅ ∆TPQ

Question 16.
Given $$\overline{A B}$$ ≅ $$\overline{C D}$$, $$\overline{A B}$$ || $$\overline{C D}$$
Prove ∆ABC ≅ ∆CDA

Question 17.
Given C is the midpoint of $$\overline{A E}$$ and $$\overline{B D}$$
Prove ∆ABC ≅ ∆EDC

Question 18.
Given $$\overline{P T}$$ ≅ $$\overline{R T}$$, $$\overline{Q T}$$ ≅ $$\overline{S T}$$
Prove ∆PQT ≅ ∆RST

In Exercises 19-22, use the given information to name two triangles that are congruent. Explain your reasoning.

Question 19.
∠SRT ≅ ∠URT, and R is the center of the circle.

Question 20.
ABCD is a square with four congruent sides and four congruent angles.

Question 21.
RSTUV is a regular pentagon.

Question 22.
$$\overline{M K}$$ ⊥ $$\overline{M N}$$, $$\overline{K L}$$ ⊥ $$\overline{N L}$$, and M and L are centers of circles.

CONSTRUCTION
In Exercises 23 and 24, construct a triangle that is congruent to ∆ABC using the SAS Congruence Theorem (Theorem 5.5).

Question 23.

Question 24.

Question 25.
ERROR ANALYSIS
Describe and correct the error in finding the value of x.

Question 26.
HOW DO YOU SEE IT?
What additional information do you need to prove that ∆ABC ≅ ∆DBC?

Question 27.
PROOF
The Navajo rug is made of isosceles triangles. You know ∠B ≅∠D. Use the SAS Congruence Theorem (Theorem 5.5 to show that ∆ABC ≅ ∆CDE. (See Example 3.)

Question 28.
THOUGHT PROVOKING
There are six possible subsets of three sides or angles of a triangle: SSS, SAS, SSA, AAA, ASA, and AAS. Which of these correspond to congruence theorems? For those that do not, give a counterexample.

Question 29.
MATHEMATICAL CONNECTIONS
Prove that
∆ABC ≅ ∆DEC
Then find the values of x and y.

Question 30.
MAKING AN ARGUMENT
Your friend claims it is possible to Construct a triangle congruent to ∆ABC by first constructing $$\overline{A B}$$ and $$\overline{A C}$$, and then copying ∠C. Is your friend correct? Explain your reasoning.

Question 31.
PROVING A THEOREM
Prove the Reflections in Intersecting Lines Theorem (Theorem 4.3).

Maintaining Mathematical Proficiency

Classify the triangle by its sides and by measuring its angles.

Question 32.

Question 33.

Question 34.

Question 35.

### 5.4 Equilateral and Isosceles Triangles

Exploration 1

Writing a Conjecture about Isosceles Triangles

Work with a partner: Use dynamic geometry software.

a. Construct a circle with a radius of 3 units centered at the origin.

b. Construct ∆ABC so that B and C are on the circle and A is at the origin.

c. Recall that a triangle is isosceles if it has at least two congruent sides. Explain why ∆ABC is an isosceles triangle.

d. What do you observe about the angles of ∆ABC?

e. Repeat parts (a)-(d) with several other isosceles triangles using circles of different radii. Keep track of your observations by copying and completing the table below. Then write a conjecture about the angle measures of an isosceles triangle.
CONSTRUCTING VIABLE ARGUMENTS
To be proficient in math, you need to make conjectures and build a logical progression of statements to explore the truth of your conjectures.

f. Write the converse of the conjecture you wrote in part (e). Is the converse true?

Question 2.
What conjectures can you make about the side lengths and angle measures of an
isosceles triangle?

Question 3.
How would you prove your conclusion in Exploration 1 (e)? in Exploration 1(f)?

### Lesson 5.4 Equilateral and Isosceles Triangles

Monitoring Progress

Copy and complete the statement.

Question 1.
If $$\overline{H G}$$ ≅ $$\overline{H K}$$, then ∠ _______ ≅ ∠ _______ .

Question 2.
If ∠KHJ ≅∠KJH, then ______ ≅ ______ .

Question 3.
Find the length of $$\overline{S T}$$ of the triangle at the left.

Question 4.
Find the value of x and y in the diagram.

Question 5.
In Example 4, show that ∆PTS ≅ ∆QTR

### Exercise 5.4 Equilateral and Isosceles Triangles

Vocabulary and Core Concept Check

Question 1.
VOCABULARY
Describe how to identify the vertex angle of an isosceles triangle.

Question 2.
WRITING
What is the relationship between the base angles of an isosceles triangle? Explain.

Monitoring Progress and Modeling with Mathematics

In Exercises 3-6. copy and complete the statement. State which theorem you used.

Question 3.
If $$\overline{A E}$$ ≅ $$\overline{D E}$$ then ∠_____ ≅ ∠_____ .

Question 4.
If $$\overline{A B}$$ ≅ $$\overline{E B}$$ then ∠_____ ≅ ∠_____ .

Question 5.
If ∠D ≅ ∠CED, then _______ ≅ _______ .

Question 6.
If ∠EBC ≅ ∠ECB, then _______ ≅ _______ .

In Exercises 7-10. find the value of x.

Question 7.

Question 8.

Question 9.

Question 10.

Question 11.
MODELING WITH MATHEMATICS
The dimensions of a sports pennant are given in the diagram. Find the values of x and y.

Question 12.
MODELING WITH MATHEMATICS
A logo in an advertisement is an equilateral triangle with a side length of 7 centimeters. Sketch the logo and give the measure of each side.

In Exercises 13-16, find the values of x and y.

Question 13.

Question 14.

Question 15.

Question 16.

CONSTRUCTION
In Exercises 17 and 18, construct an equilateral triangle whose sides are the given length.

Question 17.
3 inches

Question 18.
1.25 inches

Question 19.
ERROR ANALYSIS
Describe and correct the error in finding the length of $$\overline{B C}$$.

Question 20.
PROBLEM SOLVING
The diagram represents part of the exterior of the Bow Tower in Calgary. Alberta, Canada, In the diagram. ∆ABD and ∆CBD arc congruent equilateral triangles.

a. Explain why ∆ABC is isosceles.

b. Explain ∠BAE ≅ ∠BCE.

c. Show that ∆ABE and ∆CBE arc congruent.

d. Find the measure of ∠BAE.

Question 21.
FINDING A PATTERN
In the pattern shown. each small triangle is an equilateral triangle with an area of 1 square unit.

a. Explain how you know that an triangle made out of equilateral triangles is equilateral.
b. Find the areas of the first four triangles in the pattern.
c. Describe any patterns in the areas. Predict the area of the seventh triangle in the pattern. Explain your reasoning.

Question 22.
REASONING
The base of isosceles ∆XYZ is $$\overline{Y Z}$$. What
can you prove? Select all that apply.
(A) $$\overline{X Y}$$ ≅ $$\overline{X Z}$$
(B) ∠X ≅ ∠Y
(C) ∠Y ≅ ∠Z
(D) $$\overline{Y Z}$$ ≅ $$\overline{Z X}$$

In Exercises 23 and 24, find the perimeter of the triangle.

Question 23.

Question 24.

MODELING WITH MATHEMATICS
In Exercises 25 – 28. use the diagram based on the color wheel. The 12 triangles in the diagram are isosceles triangles with congruent vertex angles.

Question 25.
Complementary colors lie directly opposite each other on the color wheel. Explain how you know that the yellow triangle is congruent to the purple triangle.

Question 26.
The measure of the vertex angle of the yellow triangle is 30°. Find the measures of the base angles.

Question 27.
Trace the color wheel. Then form a triangle whose vertices are the midpoints of the bases of the red. yellow. and blue triangles. (These colors are the primary colors.) What type of triangle is this?

Question 28.
Other triangles can be brined on the color wheel that are congruent to the triangle in Exercise 27. The colors on the vertices of these triangles are called triads. What are the possible triads?

Question 29.
CRITICAL THINKING
Are isosceles triangles always acute triangles? Explain your reasoning.

Question 30.
CRITICAL THINKING
Is it possible for an equilateral triangle to have an angle measure other than 60°? Explain your reasoning.

Question 31.
MATHEMATICAL CONNECTIONS
The lengths of the sides of a triangle are 3t, 5t – 12, and t + 20. Find the values of t that make the triangle isosceles. Explain your reasoning.

Question 32.
MATHEMATICAL CONNECTIONS
The measure of an exterior angle of an isosceles triangle is x°. Write expressions representing the possible angle measures of the triangle in terms of x.

Question 33.
WRITING
Explain why the measure of the vertex angle of an isosceles triangle must be an even number of degrees when the measures of all the angles of the triangle are whole numbers.

Question 34.
PROBLEM SOLVING
The triangular faces of the peaks on a roof arc congruent isosceles triangles with vertex angles U and V.

a. Name two angles congruent to ∠WUX. Explain your reasoning.
b. Find the distance between points U and V.

Question 35.
PROBLEM SOLVING
A boat is traveling parallel to the shore along $$\vec{R}$$T. When the boat is at point R, the captain measures the angle to the lighthouse as 35°. After the boat has traveled 2.1 miles, the captain measures the angle to the lighthouse to be 70°.

a. Find SL. Explain your reasoning.
b. Explain how to find the distance between the boat and the shoreline.

Question 36.
THOUGHT PROVOKING
The postulates and theorems in this book represent Euclidean geometry. In spherical geometry, all points are points on the surface of a sphere. A line is a circle on the sphere whose diameter is equal to the diameter of the sphere. In spherical geometry, do all equiangular triangles have the same angle measures? Justify your answer.

Question 37.
PROVING A COROLLARY
Prove that the Corollary to the Base Angles Theorem (Corollary 5.2) follows from the Base Angles Theorem (Theorem 5.6).

Question 38.
HOW DO YOU SEE IT?
You are designing fabric purses to sell at the school fair.

a. Explain why ∆ABE ≅ ∆DCE.
b. Name the isosceles triangles in the purse.
c. Name three angles that are congruent to ∠EAD.

Question 39.
PROVING A COROLLARY
Prove that the Corollary to the Converse of the Base Angles Theorem (Corollary 5.3) follows from the Converse of the Base Angles Theorem (Theorem 5.7)

Question 40.
MAKING AN ARGUMENT
The coordinates of two points are T(0, 6) and U(6, 0) Your friend claims that points T, U, and V will always be the vertices of an isosceles triangle when V is any point on the line y = x. Is your friend correct? Explain your reasoning.

Question 41.
PROOF
Use the diagram to prove that ∆DEF is equilateral.

Given ∆ABC is equilateral
Prove ∆DEF is equilateral

Maintaining Mathematical Proficiency

Use the given property to complete the statement.

Question 42.
Reflexive Property of Congruence (Theorem 2. 1): ________ ≅ $$\overline{S E}$$

Question 43.
Symmetric Property of Congruence (Theorem 2.1): If ________ ≅ ________, then $$\overline{R S}$$ ≅ $$\overline{J K}$$

Question 44.
Transitive Property of Congruence (Theorem 2.1): If $$\overline{E F}$$ ≅ $$\overline{P Q}$$, and $$\overline{P Q}$$ ≅ $$\overline{U V}$$ ________ ≅ ________.

### 5.1 to 5.4 Quiz

Find the measure of the exterior angle.

Question 1.

Question 2.

Question 3.

Identify all pairs of congruent corresponding parts. Then write another congruence statement for the polygons.

Question 4.
∆ABC ≅ ∆DEF

Question 5.
QRST ≅ WXYZ

Decide whether enough information is given to prove that the triangles are congruent using the SAS Congruence Theorem (Thm 5.5). If so, write a proof. If not, explain why.

Question 6.

Question 7.
∆GHF, ∆KHJ

Question 8.
∆LWP, ∆NMP

Copy and complete the statement. State which theorem you used.

Question 9.
If VW ≅ WX, then ∠______ ≅ ∠ ________.

Question 10.
If XZ ≅ XY. then∠______ ≅ ∠ ________.

Question 11.
If ∠ZVX ≅∠ZXV, then ∠______ ≅ ∠ ________.

Question 12.
If ∠XYZ ≅∠ZXY, then ∠______ ≅ ∠ ________.

Find the values of x and y.

Question 13.
∆DEF ≅ ∆QRS

Question 14.

Question 15.
In a right triangle, the measure of one acute angle is 4 times the difference of the measure of the other acute angle and 5. Find the measure ol each acute angle in the triangle. (Section 5.1)

Question 16.
The figure shows a stained glass window. (Section 5.1 and Section 5.3)

a. Classify triangles 1 – 4 by their angles.

b. Classify triangles 4 – 6 by their sides.

c. Is there enough information given to prove that ∆7 ≅ ∆8? If so, label the vertices
and write a proof. If not, determine what additional information is needed.

### 5.5 Proving Triangle Congruence by SSS

Exploration 1

Drawing Triangles

Work with a partner.
Use dynamic geometry software.

a. Construct circles with radii of 2 units and 3 units centered at the origin. Label the origin A. Then draw $$\overline{B C}$$ of length 4 units.

b. Move $$\overline{B C}$$ so that B is on the smaller circle and C is on the larger circle. Then draw ∆ABC.

c. Explain why the side lengths of ∆ABC are 2, 3, and 4 units.

d. Find m∠A, m∠B, and m∠C.

e. Repeat parts (b)and (d) several times, moving $$\overline{B C}$$ to different locations. Keep track of ‘our results by copying and completing the table below. What can you conclude?
USING TOOLS STRATEGICALLY
To be proficient in math, you need to use technology to help visualize the results of varying assumptions, explore consequences, and compare predictions with data.

Question 2.
What can you conclude about two triangles when you know the corresponding sides are congruent?

Question 3.
How would you prove your conclusion in Exploration 1(e)?

### Lesson 5.5 Proving Triangle Congruence by SSS

Monitoring Progress

Decide whether the congruence statement is true. Explain your reasoning.

Question 1.
∆DFG ≅ ∆HJK

Question 2.

Question 3.
∆QPT ≅ ∆RST

Determine whether the figure is stable. Explain your reasoning.

Question 4.

Question 5.

Question 6.

Use the diagram.

Question 7.
Redraw ∆ABC and ∆DCB side by side with corresponding parts in the same position.

Question 8.
Use the information in the diagram to prove that ∆ABC ≅ ∆DCB.

### Exercise 5.5 Proving Triangle Congruence by SSS

Vocabulary and Core Concept Check

Question 1.
COMPLETE THE SENTENCE
The side opposite the right angle is called the __________of the right triangle.

Question 2.
WHICH ONE DOESNT BELONG?
Which triangles legs do not belong with the other three? Explain your reasoning.

Monitoring Progress and Modeling with Mathematics

In Exercises 3 and 4, decide whether enough information is given to prove that the triangles are congruent using the SSS Congruence Theorem (Theorem 5.8). Explain.

Question 3.
∆ABC, ∆DBE

Question 4.
∆PQS, ∆RQS

In Exercises 5 and 6, decide whether enough information is given to prove that the triangles are congruent using the HL Congruence Theorem (Theorem 5.9). Explain.

Question 5.
∆ABC, ∆FED

Question 6.
∆PQT, ∆SRT

In Exercises 7-10. decide whether the congruence statement is true. Explain your reasoning.

Question 7.
∆RST ≅ ∆TQP

Question 8.
∆ABD ≅ ∆CDB

Question 9.
∆DEF ≅ ∆DGF

Question 10.
∆JKL ≅ ∆LJM

In Exercises 11 and 12, determine whether the figure is stable. Explain your reasoning.

Question 11.

Question 12.

In Exercises 13 and 14, redraw the triangles so they are side by side with corresponding parts in the same position. Then write a proof.

Question 13.
Given $$\overline{A C}$$ ≅ $$\overline{B D}$$
$$\overline{A B}$$ ⊥ $$\overline{A D}$$
$$\overline{C D}$$ ⊥ $$\overline{A D}$$

Question 14.
Given G is the midpoint of $$\overline{E H}$$, $$\overline{F G}$$ ≅ $$\overline{G I}$$, ∠E and ∠H are right angles.
Prove ∆EFG ≅ ∆HIG

In Exercises 15 and 16. write a proof.

Question 15.
Given $$\overline{L M}$$ ≅ $$\overline{J K}$$, $$\overline{M J}$$ ≅ $$\overline{K L}$$
Prove ∆LMJ ≅ ∆JKL

Question 16.
Given $$\overline{W X}$$ ≅ $$\overline{V Z}$$, $$\overline{W Y}$$ ≅ $$\overline{V Y}$$, $$\overline{Y Z}$$ ≅ $$\overline{Y X}$$
Prove ∆VWX ≅ ∆WVZ

CONSTRUCTION
In Exercises 17 and 18, construct a triangle that is congruent to ∆QRS using the SSS Congruence Theorem Theorem 5.8).

Question 17.

Question 18.

Question 19.
ERROR ANALYSIS
Describe and correct the error in identifying congruent triangles.

Question 20.
ERROR ANALYSIS
Describe and correct the error in determining the value of x that makes the triangles congruent.

Question 21.
MAKING AN ARGUMENT
Your friend claims that in order to use the SSS Congruence Theorem (Theorem 5.8) Lo prove that two triangles are congruent, both triangles must be equilateral triangles. Is your friend correct? Explain your reasoning.

Question 22.
MODELING WITH MATHEMATICS
The distances between consecutive bases on a softball field are the same. The distance from home plate to second base is the same as the distance from first base to third base. The angles created at each base are 90°. Prove
∆HFS ≅ ∆FST ≅ ∆STH

Question 23.
REASONING
To support a tree you attach wires from the trunk of the tree to stakes in the ground, as shown in the diagram.

a. What additional information do you need to use the HL Congruence Theorem (Theorem 5.9) to prove that ∆JKL ≅ ∆MKL?
b. Suppose K is the midpoint of JM. Name a theorem you could use to prove that ∆JKL ≅ ∆MKL. Explain your reasoning.

Question 24.
REASONING
Use the photo of the Navajo rug, where $$\overline{B C}$$ ≅ $$\overline{D E}$$ and $$\overline{A C}$$ ≅ $$\overline{C E}$$

a. What additional intormation do you need to use the SSS Congruence Theorem (Theorem 5.8) to prove that ∆ABC ≅ ∆CDE?
b. What additional information do you need to use the HL Congruence Theorem (Theorem 5.9) to prove that ∆ABC ≅ ∆CDE?

In Exercises 25-28. use the given coordinates to determine whether ∆ABC ≅ ∆DEF.

Question 25.
A(- 2, – 2), B(4, – 2), C(4, 6), D(5, 7), E(5, 1), F(13, 1)

Question 26.
A(- 2, 1), B(3, – 3), C(7, 5), D(3, 6), E(S, 2), F( 10, 11)

Question 27.
A(0, 0), B(6, 5), C(9, 0), D(0, – 1), E(6, – 6), F(9, – 1)

Question 28.
A(- 5, 7), B(- 5, 2), C(0, 2), D(0, 6), E(o, 1), F(4, 1)

Question 29.
CRITICAL THINKING
You notice two triangles in the tile floor of a hotel lobby. You want to determine whether the triangles are congruent. but you only have a piece of string. Can you determine whether the triangles are congruent? Explain.

Question 30.
HOW DO YOU SEE IT?
There are several theorems you can use to show that the triangles in the “square” pattern are congruent. Name two of them.

Question 31.
MAKING AN ARGUMENT
Your cousin says that ∆JKL is congruent to ∆LMJ by the SSS Congruence Theorem (Thm. 5.8). Your friend says that ∆JKL is congruent to ∆LMJ by the HL Congruence Theorem (Thm. 5.9). Who is correct? Explain your reasoning.

Question 32.
THOUGHT PROVOKING
The postulates and theorems in this book represent Euclidean geometry. In spherical geometry. all points are points on the surface of a sphere. A line is a circle on the sphere whose diameter is equal to the diameter of the sphere. In spherical geometry. do you think that two triangles are congruent if their corresponding sides are congruent? Justify your answer.

USING TOOLS
In Exercises 33 and 34, use the given information to sketch ∆LMN and ∆STU. Mark the triangles with the given information.

Question 33.

Question 34.

Question 35.
CRITICAL THINKING
The diagram shows the light created by two spotlights, Both spotlights are the same distance from the stage.

a. Show that ∆ABD ≅ ∆CBD. State which theorem or postulate you used and explain your reasoning.
b. Are all four right triangles shown in the diagram Congruent? Explain your reasoning.

Question 36.
MATHEMATICAL CONNECTIONS
Find all values of x that make the triangles congruent. Explain.

Maintaining Mathematical proficiency

Use the congruent triangles.

Question 37.
Name the Segment in ∆DEF that is congruent to $$\overline{A C}$$.

Question 38.
Name the segment in ∆ABC that is congruent to $$\overline{E F}$$.

Question 39.
Name the angle in ∆DEF that is congruent to ∠B.

Question 40.
Name the angle in ∆ABC that is congruent to ∠F.

### 5.6 Proving Triangle Congruence by ASA and AAS

Exploration 1

Determining Whether SSA Is Sufficient

Work with a partner.
a. Use dynamic geometry software to construct ∆ABC. Construct the triangle so that vertex B is at the origin. $$\overline{A B}$$ has a length of 3 units. and $$\overline{B C}$$ has a length of 2 units.

b. Construct a circle with a radius of 2 units centered at the origin. Locate point D where the circle intersects $$\overline{A C}$$. Draw $$\overline{B D}$$.

c. ∆ABC and ∆ABD have two congruent sides and a non included congruent angle.
Name them.

d. Is ∆ABC ≅ ∆ABD? Explain your reasoning.

e. Is SSA sufficient to determine whether two triangles are congruent? Explain your reasoning.

Exploration 2

Determining Valid Congruence Theorems

Work with a partner. Use dynamic geometry software to determine which of the following are valid triangle congruence theorems. For those that are not valid. write a counter example. Explain your reasoning.
CONSTRUCTING VIABLE ARGUMENTS
To be proficient in math, you need to recognize and use counterexamples.

 Possible Congruence Theorem Valid or not valid? SSS SSA SAS AAS ASA AAA

Question 3.
What information is sufficient to determine whether two triangles are congruent?

Question 4.
Is it possible to show that two triangles are congruent using more than one congruence theorem? If so, give an example.

### Lesson 5.6 Proving Triangle Congruence by ASA and AAS

Monitoring Progress

Question 1.
Can the triangles be proven congruent with the information given in the diagram? If so, state the theorem you would use.

Question 2.
In the diagram, $$\overline{A B}$$ ⊥ $$\overline{A D}$$, $$\overline{D E}$$ ⊥ $$\overline{A D}$$, and $$\overline{A C}$$ ≅ $$\overline{D C}$$ . Prove ∆ABC ≅ ∆DEF.

Question 3.
In the diagram, ∠S ≅ ∠U and $$\overline{B D}$$$$\overline{B D}$$ . Prove that ∆RST ≅ ∆VYT

### Lesson 5.6 Proving Triangle Congruence by ASA and AAS

Vocabulary and Core Concept Check

Question 1.
WRITING
How arc the AAS Congruence Theorem (Theorem 5. 11) and the ASA Congruence
Theorem (Theorem 5.10) similar? How are they different?

Question 2.
WRITING
You know that a pair of triangles has two pairs of congruent corresponding angles. What other information do you need to show that the triangles are congruent?

Monitoring Progress and Modeling with Mathematics

In Exercises 3-6, decide whether enough information is given to prove that the triangles are congruent. If so, state the theorem you would use.

Question 3.
∆ABC, ∆QRS

Question 4.
∆ABC, ∆DBC

Question 5.
∆XYZ, ∆JKL

Question 6.
∆RSV, ∆UTV

In Exercises 7 and 8, state the third congruence statement that is needed to prove that ∆FGH ≅ ∆LMN the given theorem.

Question 7.
Given $$\overline{G H}$$ ≅ $$\overline{M N}$$, ∠G ≅ ∠M, _______ = ________
Use the AAS Congruence Theorem (Thm. 5.11).

Question 8.
Given $$\overline{F G}$$ ≅ $$\overline{L M}$$, ∠G ≅ ∠M, _______ = ________
Use the ASA Congruence Theorem (Thm. 5.10).

In Exercises 9 – 12. decide whether you can use the given information to prove that ∆ABC ≅ ∆DEF Explain your reasoning.

Question 9.
∠A ≅ ∠G, ∠C ≅∠F, $$\overline{A C}$$ ≅ $$\overline{D F}$$

Question 10.
∠C ≅ ∠F, $$\overline{A B}$$ ≅ $$\overline{D E}$$, $$\overline{B C}$$ ≅ $$\overline{E F}$$

Question 11.
∠B ≅ ∠E, ∠C ≅∠F, $$\overline{A C}$$ ≅ $$\overline{D E}$$

Question 12.
∠A ≅ ∠D, ∠B ≅∠E, $$\overline{B C}$$ ≅ $$\overline{E F}$$

CONSTRUCTION
In Exercises 13 and 14, construct a triangle that is congruent to the given triangle using the ASA Congruence Theorem (Theorem 5.10). Use a compass and straightedge.

Question 13.

Question 14.

ERROR ANALYSIS
In Exercises 15 and 16, describe and correct the error.

Question 15.

Question 16.

PROOF
In Exercises 17 and 18, prove that the triangles are congruent using the ASA Congruence Theorem (Theorem 5.10).

Question 17.
Given M is the midpoint of $$\overline{N L}$$.

Prove ∆NQM ≅ ∆MPL

Question 18.
Given $$\overline{A J}$$ ≅ $$\overline{K C}$$ ∠BJK ≅ ∠BKJ, ∠A ≅ ∠C
Prove ∆ABK ≅ ∆CBJ

PROOF
In Exercises 19 and 20, prove that the triangles are congruent using the AAS Congruence Theorem (Theorem 5.11).

Question 19.
Given $$\overline{V W}$$ ≅ $$\overline{U W}$$, ∠X ≅ ∠Z
Prove ∆XWV ≅ ∆ZWU

Question 20.
Given ∠NKM ≅∠LMK, ∠L ≅∠N
Prove ∆NMK ≅ ∆LKM

PROOF
In Exercises 21-23, write a paragraph proof for the theorem about right triangles.

Question 21.
Hypotenuse-Angle (HA) Congruence Theorem
If an angle and the hypotenuse of a right triangle are congruent to an angle and the hypotenuse of a second right triangle, then the triangles are congruent.

Question 22.
Leg-Leg (LL) Congruence Theorem
If the legs of a right triangle are congruent to the legs of a second right triangle, then the triangles are congruent.

Question 23.
Angle-Leg (AL) Congruence Theorem
If an angle and a leg of a right triangle are congruent to an angle and a leg of a second right triangle, then the triangles are Congruent.

Question 24.
REASONING
What additional in information do you need to prove ∆JKL ≅ ∆MNL by the ASA Congruence Theorem (Theorem 5. 10)?

(A) $$\overline{K M}$$ ≅ $$\overline{K J}$$
(B) $$\overline{K H}$$ ≅ $$\overline{N H}$$
(C) ∠M ≅ ∠J
(D) ∠LKJ ≅ ∠LNM

Question 25.
MATHEMATICAL CONNECTIONS
This toy contains △ABC and △DBC. Can you conclude that △ABC ≅ △DBC from the given angle measures? Explain

m∠ABC = (8x – 32)°
m∠DBC = (4y – 24)°
m∠BCA = (5x + 10)°
m∠BCD = (3y + 2)°
m∠CAB = (2x – 8)°
m∠CDB = (y – 6)°

Question 26.
REASONING
Which of the following congruence statements are true? Select all that apply.

(A) $$\overline{B D}$$ ≅ $$\overline{B D}$$
(B) ∆STV ≅ ∆XVW
(C) ∆TVS ≅ ∆VWU
(D) ∆VST ≅ ∆VUW

Question 27.
PROVING A THEOREM
Prove the Converse of the Base Angles Theorem (Theorem 5.7). (Hint: Draw an auxiliary line inside the triangle.)

Question 28.
MAKING AN ARGUMENT
Your friend claims to be able Lo rewrite any proof that uses the AAS Congruence Theorem (Thin. 5. 11) as a proof that uses the ASA Congruence Theorem (Thin. 5.10). Is this possible? Explain our reasoning.

Question 29.
MODELING WITH MATHEMATICS
When a light ray from an object meets a mirror, it is reflected back to your eye. For example, in the diagram, a light ray from point C is reflected at point D and travels back to point A. The law of reflection states that the angle of incidence, ∠CDB. is congruent to the angle of reflection. ∠ADB.

a. Prove that ∆ABD is Congruent to ∆CBD.
Given ∠CBD ≅∠ABD
DB ⊥ AC
Prove ∆ABD ≅ ∆CBD
b. Verify that ∆ACD is isosceles.
c. Does moving away from the mirror have an effect on the amount of his or her reflection a person sees? Explain.

Question 30.
HOW DO YOU SEE IT?
Name as man pairs of congruent triangles as you can from the diagram. Explain how you know that each pair of triangles is congruent.

Question 31.
CONSTRUCTION
Construct a triangle. Show that there is no AAA congruence rule by constructing a second triangle that has the same angle measures but is not congruent.

Question 32.
THOUGHT PROVOKING
Graph theory is a branch of mathematics that studies vertices and the way they are connected. In graph theory. two polygons are isomorphic if there is a one-to-one mapping from one polygon’s vertices to the other polygon’s vertices that preserves adjacent vertices. In graph theory, are any two triangles isomorphic? Explain your reasoning. second triangle that has the same angle measures but is not congruent.

Question 33.
Mathematical Connections
Six statements are given about ∆TUV and ∆XYZ

a. List all combinations of three given statements that could provide enough information to prove that ∆TUV is congruent to ∆XYZ.
b. You choose three statements at random. What is the probability that the statements you choose provide enough information to prove that the triangles are congruent?

Maintaining Mathematical proficiency

Find the coordinates of the midpoint of the line segment with the given endpoints.

Question 34.
C(1, 0) and D(5, 4)

Question 35.
J(- 2, 3) and K(4, – 1)

Question 36.
R(- 5, – 7) and S(2, – 4)

Copy and angle using a compass and straightedge.

Question 37.

Question 38.

### 5.7 Using Congruent Triangles

Exploration 1

Measuring the Width of a River

Work with a partner:
The figure shows how a surveyor can measure the width of a river by making measurements on only one side of the river.

a. Study the figure. Then explain how the surveyor can find the width of the river.

b. Write a proof to verify that the method you described in part (a) is valid.
Given ∠A is a right angle, ∠D is a right angle, $$\overline{A C}$$ ≅ $$\overline{C D}$$

c. Exchange Proofs with your partner and discuss the reasoning used.
CRITIQUING THE REASONING OF OTHERS
To be proficient in math, you need to listen to or read the arguments of others, decide whether they make sense, and ask useful questions to clarify or improve the arguments.

Exploration 2

Measuring the Width of a River

Work with a partner. It was reported that one of Napoleon’s offers estimated the width of a river as follows. The officer stood on the hank of the river and lowered the visor on his cap until the farthest thin visible was the edge of the bank on the other side. He then turned and rioted the point on his side that was in line with the tip of his visor and his eye. The officer then paced the distance to this point and concluded that distance was the width of the river.

a. Study the figure. Then explain how the officer concluded that the width of the river is EG.

b. Write a proof to verify that the conclusion the officer made is correct.
Given ∠DEG is a right angle, ∠DEF is a right angle, ∠EDG ≅ ∠EDF

c. Exchange proofs with your partner and discuss the reasoning used.

Question 3.
How can you use congruent triangles to make an indirect measurement?

Question 4.
Why do you think the types of measurements described in Explorations 1 and 2 are called indirect measurements?

### Lesson 5.7 Using Congruent Triangles

Monitoring Progress

Question 1.
Explain how you can prove that ∠A ≅ ∠C.

Question 2.
In Example 2, does it mailer how far from point N you place a stake at point K? Explain.

Question 3.
Write a plan to prove that ∆PTU ≅ ∆UQP.

Question 4.
Use the construction of an angle bisector on page 42. What segments can you assume are congruent?

### Exercise 5.7 Using Congruent Triangles

Vocabulary and core concept check

Question 1.
COMPLETE THE SENTENCE
_____________ parts of congruent triangle are congruent.

Question 2.
WRITING
Describe a situation in which you might choose to use indirect measurement with
congruent triangles to find a measure rather than measuring directly.

Monitoring Progress and Modeling With Mathematics

In Exercise 3-8, explain how to prove that the statement is true.

Question 3.
∠A ≅ ∠D

Question 4.
∠Q ≅∠T

Question 5.
$$\overline{J M}$$ ≅ $$\overline{L M}$$

Question 6.
$$\overline{A C}$$ ≅ $$\overline{D B}$$

Question 7.
$$\overline{G K}$$ ≅ $$\overline{H J}$$

Question 8.
$$\overline{Q W}$$ ≅ $$\overline{V T}$$

In Exercises 9-12, write a plan to prove that ∠1 ≅∠2.

Question 9.

Question 10.

Question 11.

Question 12.

In Exercises 13 and 14. write a proof to verify that the construction is valid.

Question 13.
Line perpendicular to a line through a point not on the line

Plan for proof ∆APQ ≅ ∆BPQ by the congruence Theorem (Theorem 5.8). Then show the ∆APM ≅ ∆BPM using the SAS Congruence Theorem (Theorem 5.5). Use corresponding parts of congruent triangles to show that ∠AMP and ∠BMP are right angles.

Question 14.
Line perpendicular to a line through a p0int on the line

Plan for Proof Show that ∆APQ ≅ ∆BPQ by the SSS Congruence Theorem (Theorem 5.8) Use corresponding parts of congruent triangles to show that ∠QPA and ∠QPB are right angles.

In Exercises 15 and 16, use the information given in the diagram to write a proof.

Question 15.
Prove $$\overline{F L}$$ ≅ $$\overline{H N}$$

Question 16.
Prove ∆PUX ≅ ∆QSY

Question 17.
MODELING WITH MATHEMATICS
Explain how to find the distance across the canyon.

Question 18.
HOW DO YOU SEE IT?
Use the tangram puzzle.

a. Which triangle(s) have an area that is twice the area of the purple triangle?
b. How man times greater is the area of the orange triangle than the area of the purple triangle?

Question 19.
PROOF
Prove that the green triangles in the Jamaican flag congruent if $$\overline{A D}$$ || $$\overline{B C}$$ and E is the midpoint of $$\overline{A C}$$.

Question 20.
THOUGHT PROVOKING
The Bermuda Triangle is a region in the Atlantic Ocean in which many ships and planes have mysteriously disappeared. The vertices are Miami. San Juan. and Bermuda. Use the Internet or some other resource to find the side lengths. the perimeter, and the area of this triangle (in miles). Then create a congruent triangle on land using cities as vertices.

Question 21.
MAKING AN ARGUMENT
Your friend claims that ∆WZY can be proven congruent to ∆YXW using the HL Congruence Theorem (Thm. 5.9). Is your friend correct? Explain your reasoning.

Question 22.
CRITICAL THINKING
Determine whether each conditional statement is true or false. If the statement is false, rewrite it as a true statement using the converse, inverse, or contrapositive.
a. If two triangles have the same perimeter, then they are congruent.
b. If two triangles are congruent. then they have the same area.

Question 23.
ATTENDING TO PRECISION
Which triangles are congruent to ∆ABC? Select all that apply.

Maintaining Mathematical Proficiency

Find the perimeter of the polygon with the given vertices.

Question 24.
A(- 1, 1), B(4, 1), C(4, – 2), D(- 1, – 2)

Question 25.
J(- 5, 3), K(- 2, 1), L(3, 4)

### 5.8 Coordinate Proofs

Exploration 1

Writing a coordinate Proof

Work with a partner.

a. Use dynamic geometry software to draw $$\overline{A B}$$ with endpoints A(0, 0) and B(6, 0).

b. Draw the vertical line x = 3.

c. Draw ∆ABC so that C lies on the line x = 3.

d. Use your drawing to prove that ∆ABC is an isosceles triangle.

Exploration 2

Writing a Coordinate proof

Work with a partner.

a. Use dynamic geometry software to draw $$\overline{A B}$$ with endpoints A(0, 0) and B(6, 0).

b. Draw the vertical line x = 3.

c. Plot the point C(3, 3) and draw ∆ABC. Then use your drawing to prove that ∆ABC is an isosceles right triangle.

d. Change the coordinates of C so that C lies below the x-axis and ∆ABC is an isosceles right triangle.

e. Write a coordinate proof to show that if C lies on the line x = 3 and ∆ABC is an isosceles right triangle. then C must be the point (3, 3) or the point found in part (d).
CRITIQUING THE REASONING OF OTHERS
To be proficient in math, you need to understand and use stated assumptions, definitions, and previously established results.

Question 3.
How can you use a coordinate plane to write a proof?

Question 4.
Write a coordinate proof to prove that ∆ABC with vertices A(0, 0), 8(6, 0), and C(3, 3√3) is an equilateral triangle.

### Lesson 5.8 Coordinate Proofs

Monitoring Progress

Question 1.
Show another way to place the rectangle in Example 1 part (a) that is convenient
for finding side lengths. Assign new coordinates.

Question 2.
A square has vertices (0, 0), (m, 0), and (0, m), Find the fourth vertex.

Question 3.
Write a plan for the proof.
Given $$\vec{G}$$J bisects ∠OGH.
Proof ∆GJO ≅ ∆GJH

Question 4.
Graph the points 0(0, 0), H(m, n), and J(m, 0). Is ∆OHJ a right triangle? Find the side lengths and the coordinates of the midpoint of each side.

Question 5.
Write a coordinate proof.

Given Coordinates of vertices of ∆NPO and ∆NMO
Prove ∆NPO ≅ ∆NMO

### Exercise 5.8 Coordinate Proofs

Vocabulary and Core Concept Check

Question 1.
VOCABULARY
How is a coordinate proof different from other types of proofs you have studied?
How is it the same?

Question 2.
WRITING
Explain why it is convenient to place a right triangle on the grid as shown when writing a coordinate proof.

Maintaining Progress and Modeling with Mathematics

In Exercises 3-6, place (he figure in a coordinate plane in a convenient way. Assign coordinates to each vertex. Explain the advantages of your placement.

Question 3.
a right triangle with leg lengths of 3 units and 2 units

Question 4.
a square with a side length of 3 units

Question 5.
an isosceles right triangle with leg length p

Question 6.
a scalene triangle with one side length of 2m

In Exercises 7 and 8, write a plan for the proof.

Question 7.
Given Coordinates of vertices of ∆OPM and ∆ONM Prove ∆OPM and ∆ONM are isosceles triangles.

Question 8.
Given G is the midpoint of $$\overline{H F}$$.
Prove ∆GHJ ≅ ∆GFO

In Exercises 9-12, place the figure in a coordinate plane and find the indicated length.

Question 9.
a right triangle with leg lengths of 7 and 9 units; Find the length of the hypotenuse.

Question 10.
an isosceles triangle with a base length of 60 units and a height of 50 units: Find the length of one of the legs.

Question 11.
a rectangle with a length o! 5 units and a width of 4 units: Find the length of the diagonal.

Question 12.
a square with side length n: Find the length of the diagonal.

In Exercises 13 and 14, graph the triangle with the given vertices. Find the length and the slope of each side of the triangle. Then find the coordinates of the midpoint of each side. Is the triangle a right triangle? isosceles? Explain. Assume all variables are positive and in m ≠ n.)

Question 13.
A(0, 0), B(h, h), C(2h, 0)

Question 14.
D(0, n), E(m, n), F(m, 0)

In Exercises 15 and 16, find the coordinates of any unlabeled vertices. Then find the indicated length(s).

Question 15.
Find ON and MN.

Question 16.
Find OT.

PROOF
In Exercises 17 and 18, rite a coordinate proof.

Question 17.
Given Coordinates of vertices of ∆DEC and ∆BOC
Prove ∆DEC ≅ ∆BOC

Question 18.
Given Coordinates of ∆DEA, H is the midpoint of $$\overline{D A}$$, G is the mid point of $$\overline{E A}$$
Prove $$\overline{D G}$$ ≅ $$\overline{E H}$$

Question 19.
MODELING WITH MATHEMATICS
You and your cousin are camping in the woods. You hike to a point that is 500 meters cast and 1200 meters north of the Campsite. Your cousin hikes to a point that is 1000 meters cast of the campsite. Use a coordinate proof to prove that the triangle formed by your Position, your Cousin’s position. and the campsite is isosceles. (See Example 5.)

Question 20.
MAKING AN ARGUMENT
Two friends see a drawing of quadrilateral PQRS with vertices P(0, 2), Q(3, – 4), R(1, – 5), and S(- 2, 1). One friend says the quadrilateral is a parallelogram but not a rectangle. The other friend says the quadrilateral is a rectangle. Which friend is correct? Use a coordinate proof to support your answer.

Question 21.
MATHEMATICAL CONNECTIONS
Write an algebraic expression for the coordinates of each endpoint of a line segment whose midpoint is the origin.

Question 22.
REASONING
The vertices of a parallelogram are (w, 0), (o, v), (- w, 0), and (0, – v). What is the midpoint of the side in Quadrant III?
(a) $$\left(\frac{w}{2}, \frac{v}{2}\right)$$
(b) $$\left(-\frac{w}{2},-\frac{v}{2}\right)$$
(c) $$\left(-\frac{w}{2}, \frac{v}{2}\right)$$
(d) $$\left(\frac{w}{2},-\frac{v}{2}\right)$$

Question 23.
REASONING
A rectangle with a length of 3h and a width of k has a vertex at (- h, k), Which point cannot be a vertex of the rectangle?
(A) (h, k)
(B) (- h, 0)
(c) (2h, 0)
(D) (2h, k)

Question 24.
THOUGHT PROVOKING
Choose one of the theorems you have encountered up to this point that you think would be easier to prove with a coordinate proof than with another type of proof. Explain your reasoning. Then write a coordinate proof.

Question 25.
CRITICAL THINKING
The coordinates of a triangle are (5d – 5d), (0, – 5d), and (5d, 0). How sh
would the coordinates be changed to make a coordinate proof easier to complete?

Question 26.
HOW DO YOU SEE IT?
without performing any calculations, how do you know that the diagonals of square TUVW are perpendicular to each oilier? How can you use a similar diagram to show that the diagonals of any square are perpendicular to each other?

Question 27.
PROOF
Write a coordinate proof for each statement.
a. The midpoint o! the hypotenuse of a right triangle is the same distance from each vertex of the triangle.
b. Any two congruent right isosceles triangles can be combined to form a single isosceles triangle.

Maintaining Mathematical proficiency

$$\vec{Y}$$W bisects ∠XYZ such that m∠XYW = (3x – 7)° and m∠WYZ = (2x + 1)°.

Question 28.
Find the value of x.

Question 29.
Find m∠XYZ

### 5.1 Angles of Triangles

Question 1.
Classify the triangle at the right by its sides and by measuring its angles.

Find the measure of the exterior angle.

Question 2.

Question 3.

Find the measure of each acute angle.

Question 4.

Question 5.

### 5.2 Congruent Polygons

Question 6.
In the diagram. GHJK ≅ LMNP. Identify all pairs of congruent corresponding parts. Then write another congruence statement for the quadrilaterals.

Question 7.
Find m ∠ V.

### 5.3 Proving Triangle Congruence by SAS

Decide whether enough information is given to prove that ∆WXZ ≅ ∆YZX using the SAS Congruence Theorem (Theorem 5.5). If so, write a proof. If not, explain why.

Question 8.

Question 9.

### 5.4 Equilateral and Isosceles Triangles

Copy and Complete the statement.

Question 10.
If $$\overline{Q P}$$ ≅ $$\overline{Q R}$$, then ∠ ______ ≅ ∠ ______ .

Question 11.
If ∠TRV ≅ ∠TVR, then ______ ≅ ______ .

Question 12.
If $$\overline{R Q} \cong \overline{R S}$$, then ∠ ______ ≅ ∠ ______ .

Question 13.
If ∠SRV ≅ ∠SVR, then ______ ≅ ______ .

Question 14.
Find the values of x and y in the diagram.

### 5.5 Proving Triangle Congruence by SSS

Question 15.
Decide whether enough information is given to prose that ∆LMP ≅ ∆NPM using the SSS Congruence Theorem (Thin. 5.8). If so, write a proof. If not, explain why.

Question 16.
Decide whether enough information is given to prove that ∆WXZ ≅ ∆YZX using the HL Congruence Theorem (Thm. 5.9). If so, write a proof. If not, explain why.

### 5.6 Proving Triangle Congruence by ASA and AAS

Question 17.
∆EFG, ∆HJK

Question 18.
∆TUS, ∆QRS

Decide whether enough information is given to prove that the triangles are congruent using the ASA Congruence Theorem (Thm. 5.10). If so, write a proof, If not, explain why.

Question 19.
∆LPN, ∆LMN

Question 20.
∆WXZ, ∆YZX

### 5.7 Using Congruent Triangles

Question 21.
Explain how to prove that ∠K ≅∠N.

Question 22.
Write a plan to prkove that ∠1 ≅ ∠2

### 5.8 Coordinate Proofs

Question 23.
Write a coordinate proof.
Given Coordinates of vertices of quadrilateral OPQR
Prove ∆OPQ ≅ ∆QRO

Question 24.
Place an isosceles triangle in a coordinate plane in a way that is convenient for finding side lengths. Assign coordinates to each vertex.

Question 25.
A rectangle has vertices (0, 0), (2k, 0), and (0, k), Find the fourth vertex.

### Congruent Triangles Test

Write a Proof.

Question 1.
Given $$\overline{C A} \cong \overline{C B} \cong \overline{C D} \cong \overline{C E}$$
Prove ∆ABC ≅ ∆EDC

Question 2.
Given $$\overline{J K}\|\overline{M L}, \overline{M J}\| \overline{K L}$$
Prove ∆MJK ≅ ∆KLM

Question 3.
Gven \overline{Q R} \cong \overrightarrow{R S}, ∠P ≅ ∠T
Prove ∆SRP ≅ ∆QRT

Question 4.
Find the measure of each acute angle in the figure at the right.

Question 5.
Is it possible to draw an equilateral triangle that is not equiangular? If so, provide an example. If not, explain why.

Question 6.
Can you use the Third Angles Theorem (Theorem 5.4) to prove that two triangles are congruent? Explain your reasoning.

Write a plan through that ∠1 ≅∠2

Question 7.

Question 8.

Question 9.
Is there more than one theorem that could be used to prove that ∆ABD ≅ ∆CDB? If so, list all possible theorems.

Question 10.
Write a coordinate proof t0 show that the triangles created b the keyboard stand are congruent.

Question 11.
The picture shows the Pyramid of Cestius. which is located in Rome, Italy. The measure of the base for the triangle shown is 100 Roman feet. The measures of the other two sides of the triangle are both 144 Roman feet.

a. Classify the triangle shown by its sides.

b. The measure of ∠3 is 40° What are the measures of ∠1 and ∠2? Explain your reasoning.

### Congruent Triangles Cumulative Assessment

Question 1.
Your friend claims that the Exterior Angle Theorem (Theorem 5.2) can be used to prove the Triangle Sum Theorem (Theorem 5, 1). Is your friend correct? Explain your reasoning.

Question 2.
Use the steps in the construction to explain how you know that the line through point P is parallel to line m.

Question 3.
The coordinate plane shows ∆JKL and ∆XYZ

a. Write a composition of transformations that maps ∆JKL to ∆XYZ

b. Is the composition a congruence transformation? If so, identify all congruent corresponding parts.

Question 4.
The directed line segment RS is shown. Point Q is located along $$\overline{R S}$$ so that the ratio of RQ to QS is 2 to 3. What are the coordinates of point Q?

(A) Q(1, 2, 3)
(B) Q(4, 2)
(C) Q(2, 3)
(D) Q(-6, 7)

Question 5.
The coordinate plane shows that ∆ABC and ∆DEF

a. Prove ∆ABC ≅ ∆DEF using the given information.

b. Describe the composition of rigid motions that maps ∆ABC to ∆DEF

Question 6.
The vertices of a quadrilateral are W(0, 0), X(- 1, 3), )(2, 7), and Z(4, 2). Your friend claims that point W will not change after dilatinig quadrilateral WXYZ by a scale factor of 2. Is your friend correct? Explain your reasoning.

Question 7.
Which figure(s) have rotational symmetry? Select all that apply.
(A)
(B)
(C)
(D)