Complementary angles are two angles
up to a right angle
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°
How to Find a Complementary Angle
What is the missing angle θ below?
The 53° angle and θ are complementary angles. They add up to 90°.
53° + θ = 90°
the 53° angle from 90°.
θ = 90° − 53° = 37°
The missing angle θ is 37°.
The slider below shows another real example of complementary angles.
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.