
"The sum of the measures of the angles of a triangle is 180°". In ABC, mÐA + mÐb + mÐc = 180^{0} In the above triangle the sum of three angles is: 70 + 60 + 50 = 180^{0} Examples:
Directions: Answer the following questions. 1) Prove triangle sum theorem. 2) Prove the corollary to the triangle sum theorem: The acute angles of a right triangles are complementary. 3) Draw the triangles with the following measures, use a protractor to measure angles : 60^{0}60^{0}60^{0} triangle, 50^{0}70^{0}60^{0} triangle, 40^{0} 50^{0} 90^{0} triangle 30^{0} 60^{0} 90^{0} triangle 45^{0} 45^{0} 90^{0} triangle 20^{0} 50^{0} 180^{0} triangle 120^{0} 20^{0} 40^{0} triangle 140^{0} 10^{0} 30^{0} triangle 160^{0} 10^{0} 10^{0} triangle 4) Draw 5 triangles and measure the interior angles using a protractor and prove that the sum of the measures is 180 degrees. 