Complementary Angles – Pairs That Add to 90°

Two angles are complementary if their measures add up to exactly 90° – a right angle. The two angles don't need to be next to each other or drawn in any particular way; the only requirement is that their measures sum to 90°. To find the complement of a known angle, simply subtract it from 90°.

“Complementary” comes from the Latin complementum, meaning “that which completes” – a complementary angle is exactly what's needed to complete the pair into a full right angle.

Finding a Complement

Real-Life Application

• Carpentry joints: some corner joints are designed using complementary angle cuts.
• Ramps and staircases: a ramp's incline and its complement describe the space it occupies.
• Optics: some mirror and lens setups rely on complementary angle relationships.

Key Takeaways

Practice: Complementary Angles