Angles are unions of two rays that have the same endpoint. The rays are the sides of the angle, and the endpoint is the vertex. Angles are measured in degrees. The following are types of angles:

Acute Angle

Angles less than 90 degrees.

Right Angle

Angles 90 degrees. These are often signified with a box in the corner.

Obtuse Angle

Angles more than 90 degrees.

Complementary Angles

Are two angles whose sum is 90 degrees.

Supplementary Angles

Are two angles whose sum is 180 degrees.

If you know one angle of either a complementary or supplementary angle it is easy to discover the other. Simply subtract the angle from 180 or 90 depending on the angle. For example: