The size of interior angles of a polygon is given by: [(n-2)180]/n where n is the number of sides. given that the exterior angle is 120°, the interior angle will be: x+120=180 x=180-120 x=60° thus plugging t=in the above formula and solving for n we get: [(n-2)180]/n=60 (n-2)180=60n 180n-360=60n 180n-60n=360 120n=360 n=360/120 n=3 thus the polygon is a 3 sided polygon, otherwise known as triangle.
