Supplementary Angles

Two Angles are Supplementary when they add up to 180 degrees.

These two angles (140° and 40°) are Supplementary Angles, because they add up to 180°:

Notice that together they make a straight angle.

But the angles don't have to be together.

These two are supplementary because
60° + 120° = 180°

Complementary vs Supplementary

A related idea is Complementary Angles, they add up to 90°

How to remember which is which? Easy! Think:

• "C" of Complementary stands for "Corner"  (a Right Angle), and
• "S" of Supplementary stands for "Straight" (180 degrees is a straight line)

You can also think "Supplement" (like a Vitamin Supplement) is something extra, so it is bigger.