Question

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.

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