Supplementary Angles

Supplementary Angles

Supplementary angles are two angles which add up to a straight angle (180°).

Two angles that add to 180° are are said to supplement each other.

A Real Example of Supplementary Angles

Angles of 100° and 80° are supplementary angles.

100° + 80° = 180°

How to Find a Supplementary Angle


What is the missing angle θ below?



The 56° angle and θ are supplementary angles. They add up to 180°.

56° + θ = 180°


Subtract the 56° angle from 180°.

θ = 180° − 56° = 124°


The missing angle θ is 124°.


The slider below shows another real example of supplementary angles.

Open the slider in a new tab

See Also

What is an angle? What is a straight angle? The interior angles of a polygon The exterior angles of a polygon What is a right angle? What is an acute angle? What is an obtuse angle?