What is the measure of an exterior angle of a 25-gon? And what is the formula to figure this out?

Answer 1

A LOGO "turtle" would start at the lower left of the 25-gon, move a fixed amount to the right, turn left the amount of the exteral angle, move forward the fixed amount, turn left the amount of the external angle, ... move to the starting position, and turn left the external angle amount.

The total of the 25 turn-left angles is 360° (that is, it has completely turned around).

An exteral angle is 360/25.