Polygonal Exterior Angle
Imagine drawing a polygon with a pencil. While drawing a straight line with a pencil, We change the direction at the vertex. The size of the angle changing direction at the vertex becomes 'exterior angle.'
If you turn around and return to the original position, the process of drawing the polygon is finished.
During one round return, the sum of the angles changed is 360°.
Therefore, no matter what shape polygon is drawn, the sum of the exterior angles is always 360˚.
However, for this law to be true, there must be no concave portions of the polygon's vertices.