Angle Sum Theorem
The Angle Sum Theorem gives an important result about triangles, which is used in many algebra and geometry problems. We give the proof below.
Theorem: The sum of the measures of the interior angles of a triangle is .
Construct a line parallel to through point . Call this line
|Angle Addition Postulate|
|Linear Pair Postulate|
|Alternate Interior Angles Theorem|
|Definition of Congruence|