The interior angle of a regular polygon is 20° more than three times the exterior angle.find the number of sides of the polygon?
at any vertex, the sum of the interior and the exterior must is 189°
exterior angle --- x
interior angle = 3x+20
3x+20 + x = 180
4x =160
x = 40
let the number of sides be n
40n = 360
n = 9
you have a nonagon.