Lesson: Interior and Exterior Angles of Triangles Mathematics • First Year of Preparatory School

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In this lesson, we will learn how to complete geometric proofs using the angle sum of a triangle and find interior and exterior angles of triangles.

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.