To find the value of a given exterior angle of a regular polygon, simply divide 360 by the number of sides or angles that the polygon has. For example, an eight-sided regular polygon, an octagon, has exterior angles that are 45 degrees each, because 360/8 = 45.
If each interior angle is 8 times the degree measure of each exterior angle how many sides does the polygon have. Now 8+1 = 9. Divide 180 by 9 to get 20.
