SUPPLEMENTARY ANGLES
Definition Of Supplementary Angles
Supplementary angles are two angles that add up to give a straight angle, 180°
Example of Supplementary Angles
In the example shown, 125° and 55° add up to give 180°, so they are called supplementary angles.
Video Examples:Supplementary Angles
Solved Example on Supplementary Angles
Ques: ∠A and ∠B are supplementary angles and ∠A = ∠B. What are the measures of ∠A and ∠B?
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 ∠A and ∠B are supplementary angles and m∠A = m∠B.
Step 3: Let m∠A = m∠B = x, then m∠A + m∠B = 180°
Step 4: x + x = 180° [Substitute ∠A = ∠B = x in step 2.]
Step 5: 2x = 180°
Step 6: 
[Divide by 2.]
Step 7: So, m∠A = m∠B = 90°
Quick Summary
- Supplementary angles add up to 180°.
- If two angles form a straight line, they are supplementary.
🍎 Teacher Insights
Use real-world examples like a straight line or a protractor to demonstrate supplementary angles. Encourage students to draw diagrams.🎓 Prerequisites
- Angles
- Degrees
- Basic Algebra
Check Your Knowledge
Q1: If angle X is 70°, what is its supplementary angle?
Q2: Which pair of angles are supplementary?
Frequently Asked Questions
Q: What is the supplement of a 60° angle?
A: 120°, because 60° + 120° = 180°.
Q: Can supplementary angles be acute?
A: No, at least one angle must be obtuse or right.