What Are Supplementary Angles? | HowStuffWorks

Complementary and supplementary angles are two important aspects of geometry that help people navigate and visualize space. However, unless you’ve dusted off your high school textbooks lately, these concepts are likely fuzzy memories of a bygone era.

Although complementary and supplementary angles both involve combining two different angles, they vary slightly. Two complementary angles add up to 90 degrees (a right angle), while larger combinations called supplementary angles add up to 180 degrees (a straight line).

The difference between complementary and supplementary angles boils down to the sum of two angles needed to create these shapes. Two acute angles can combine to form a right angle (complementary), while two obtuse angles will create a third angle larger than 180 degrees (nonsupplementary).