Sum of the three exterior angles =(∠1+∠2)+(∠2+∠3)+(∠3+∠1) =2(∠1+∠2+∠3) (Sum of the interior angles are 180°) =2×180°=360° Sum of exterior angles of any polygon =360° Alternate Method Sum of the Exterior angles =(180°−∠A)+(180°−∠B)+(180°−∠C) =540°−(∠A+∠B+∠C) =540°−180° Sum of angles of a triangle is 180°) =360°