# Lesson Plan: Interior and Exterior Angles of Triangles Mathematics

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to complete geometric proofs using the angle sum of a triangle and find interior and exterior angles of triangles.

#### Objectives

Students will be able to

• prove that the sum of the measures of the interior angles of a triangle is equal to ,
• use the angle sum of a triangle to prove other geometric results,
• understand that the exterior angle of a triangle is the supplementary angle to the adjacent interior angle,
• understand and prove that the measure of the exterior angle of a triangle is equal to the sum of the measures of the two opposite interior angles,
• find the measure of missing angles using the property of an exterior angle of a triangle being equal to the sum of the measures of the opposite interior angles,
• find the sum of the measures of the exterior angles of a triangle.

#### Prerequisites

Students should already be familiar with

• the concept of an exterior angle,
• the angle sum of a triangle,
• parallel lines and traversals.

#### Exclusions

Students will not cover