Supplementary Angles
Definition of Supplementary Angles
- Supplementary angles are two angles that add up to give a straight angle, 180°.
Examples of Supplementary Angles
- In the example shown, 125° and 55° add up to give 180°, so they are called supplementary angles.
Solved Example on Supplementary Angles
and 
are supplementary angles and 
= 
. What are the measures of 
and 
?
Choices:
A. 60°,120°
B. 180°, 180°
C. 45°, 45°
D. 90°, 90°
Correct answer: D
Solution:
Step 1: Supplementary angles are two angles that add up to give a straight angle, 180°.
Step 2: Given 
and 
are supplementary angles and m = m .
Step 3: Let 
then 
Step 4: x + x = 180° [Substitute 
=
= x in step 2.]
Step 5: 2x = 180°
Step 6: 
[Divide by 2.]
Step 7: So, 
