# Supplementary Angles

## What Are Supplementary Angles?

When two angles add up to 180 degrees they are called

**Supplementary Angles**. For an example, closely look at the diagram below. We have a straight line which is a 180° angle. This 180° angle is cut in two by ray

**EF**. So now the 180° is divided in to two smaller angles that add up to 180°. Now let us express this definition in geometric math terms. Supplementary angles in geometry have the following characteristics.

- First let's start with a Straight Angle:
**∠DEC**. We already know that Straight Angle are 180°. - Now let us draw a Ray
**EF**. The angle at**∠FEC**is 33°. - If we look at the diagram below, the two adjacent angles
are
**∠DEF**and**d∠FEC**. The sum of these two angles are 180° because they form a Straight Angle. - We know 180° minus
**∠FEC**equals**∠DEF**.**∠FEC**equals 33°. So 180° minus 33° equals 147°. So the angle at**∠DEF**equals 147°.