Question 765694
The Exterior Angle is the angle between any side of a shape,
and a line extended from the next side.

when you add up the Interior Angle and Exterior Angle you get a straight line, {{{180}}}°-Supplementary Angles

 it's proven that the sum of a triangle's angles, no matter what, always total 180 degrees. Because all polygons consist of triangles, the (number of sides - 2) multiplied by {{{180}}} is the total angle measure

or, the exterior angles add up to one full revolution (which is {{{360}}}°)