Sum of the three exterior angles of a triangle is __________

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

⇒ ∠A + ∠B = external ∠C

∠A + ∠C = external ∠B

∠C + ∠B = external ∠A

Adding above three, we get

2∠A + 2 ∠B + 2∠C = sum of the three external angles

⇒ 2(∠A + ∠B + ∠C) = sum of the three external angles

We know that the sum of the angles of a triangle is 180°.

⇒ 2× 180° = sum of the three external angles

⇒ Sum of the three external angles = 4 × 90°