## The Lesson

Complementary angles are two angles which add up to a right angle (90°). Two angles that add to 90° are are said to complement each other.

## A Real Example of Complementary Angles

Angles of 30° and 60° are complementary angles.
30° + 60° = 90° ## Question

What is the missing angle θ below? # 1

The 53° angle and θ are complementary angles. They add up to 90°.
53° + θ = 90°

# 2

Subtract the 53° angle from 90°.
θ = 90° − 53° = 37°

The missing angle θ is 37°.

## Lesson Slides

The slider below shows another real example of complementary angles. Open the slider in a new tab

## What Types of Angles Are Complementary?

Complementary angles form a Corner.

## What's In an Name?

Complementary comes from the Latin word "complementum" meaning "fill up, complete, supply. This is because an acute angle is filled up to form a right angle. We get the word "complete" from the same root. Don't confuse a complementary angle with a complimentary angle; which would be a free angle or an angle giving praise.

## Complementary Angles Are Acute Angles

Both complementary angles are less than 90°, and so are acute angles.