Overview
This lecture explains the concept of complementary angles and demonstrates how to find a missing angle when the two angles must add up to 90 degrees.
Complementary Angles
- Complementary angles are two angles whose measures add up to 90 degrees.
- If the sum of two angles is 90 degrees, they are called complementary.
Finding a Missing Complementary Angle
- To find a missing angle, subtract the known angle from 90 degrees.
- Example: If one angle is 25°, the missing angle is 90° − 25° = 65°.
- Example: If one angle is 72°, the missing angle is 90° − 72° = 18°.
- You can check your answer by adding the two angles to see if they total 90°.
Steps for Solving
- Write the equation: (given angle) + (missing angle) = 90°.
- Rearrange: (missing angle) = 90° − (given angle).
- Calculate using either mental math or written subtraction.
Checking Your Work
- Always add your found angles together to confirm they equal 90°.
- If they do, your solution is correct.
Key Terms & Definitions
- Complementary angles — Two angles whose measures add up to exactly 90 degrees.
Action Items / Next Steps
- Practice solving problems involving complementary angles by subtracting from 90°.
- Double check your answers by adding the two angles together.