Key Idea: Sum of Angles in a Triangle

The sum of the interior angles of any triangle is always:

180∘

General Rule:

Angle 1+ Angle 2+ Angle 3 = 180∘
Applies to all triangles: scalene, isosceles, and equilateral.

• Can be used to find a missing angle if the other two are known.

Why this matters for the SAT:

Triangle angle sums appear frequently in geometry problems.
Knowing this rule allows you to quickly solve for missing angles and check your work.