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

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.