Title: Lesson 13-2
Author: mark_cameron
Last saved by: gtsmith
Company: McGraw-Hill

Lesson 9-3

Example 1 Find a Missing Angle Measure

80°

x°

Find the value of x in the figure. 

The angle labeled x° and the angle labeled 80° are vertical angles. Therefore, they are congruent. So, the value of x is 80.

Example 2 Classify Pairs of Angles
Classify the pair of angles as complementary, supplementary, or neither.

45°

135°

135° + 45° = 180°
Since the sum of their measures is 180°, the angles are supplementary.

Example 3 Classify Pairs of Angles
Classify the pair of angles as complementary, supplementary, or neither.

30°

60°

30° + 60° = 90°
Since the sum of their measures is 90°, the angles are complementary.

Example 4 Find Missing Angle Measures
Find the value of x in the figure.

15°

x°

	Since the angles form a right angle, 
	they are complementary.

  15° + x° = 90°	Definition of complementary angles
15° + 75° = 90°	THINK What measure added to 15° equals 90°?

So, the value of x is 75.

Example 5 Find Missing Angle Measures
Find the value of x in the figure.

45°

x°

	Since the angles form a straight line, 
	they are supplementary.

    45° + x° = 180°	Definition of supplementary angles
45° + 135° = 180°	THINK What measure added to 45° equals 180°?

So, the value of x is 135.