Let the three angles are x, y, z. One angle of a triangle is equal to the sum of the other two equal angles. x = (y + z) We know that sum of three angles of a triangle = 180° So, we write, x + y + z = 180° ⇒ x + x = 180° ⇒ x = 180°/2 = 90° As we are seeing that one of the angles of the triangle is right angle then it is right angled triangle.