Key Idea: Supplementary Angles

Supplementary angles are two angles whose sum is 180°.
They often appear as angles that form a straight line.

General Rule:

Angle 1 + Angle 2 = 180∘

• Each angle is called the supplement of the other.

• Can be used to find a missing angle when one is known.

Why this matters for the SAT:

Supplementary angles frequently appear in geometry problems, including lines, triangles, and polygons.
Recognizing this relationship helps solve for unknown angles quickly.