Question

An exterior angle of a triangle is 120° and one of the interior opposite angles is 30°. Find the other angles of the triangle.

Answer 1

Given: ∠ACD = 120° and ∠ABC = 30°

To Find: ∠A and ∠C

We know that an exterior angle is equal to the sum of its interior opposite angles.

∠A + ∠B = ∠ACD

∠A + 30° = 120°

∠A = 120° − 30°

∴∠A = 90°

Also, ∠ACD + ∠ACB = 180° (Linear angles)

120° + ∠ACB = 180°

∠ACB = 180° − 120°

∴∠ACB = 60°