the measure of third angle of the triangle is 40° step-by-step explanation: given : measure of two angles of a triangle as 90° and 50° we have to find the measure of the third angle of the triangle. angle sum property of a triangle states that the sum of angles of a triangle is always 180° let for the given triangle abc, with m∠a = 90° and m∠b = 50° then according to angle sum property stated above, ∠a + ∠b + ∠c = 180° 90° + 50° + ∠c = 180° 140° + ∠c = 180° ∠c = 180° - 140° simplify, we get, ∠c = 40° thus, the measure of third angle of the triangle is 40°