Answer:
18
Step-by-step explanation:
The interior and exterior angle of a polygon is supplementary
let interior be I
let exterior be E
I + E = 180
Since the interior angle is 8 times that of an exterior angle,
8E + E = 180 [replacing I with 8E]
9E = 180
E = 20
The exterior angle is 20 degrees
I + E = 180
I + 20 = 180
I = 160
The interior angle is 160 degrees.
The equation to find the interior angle of a polygon with 'n' number of sides is:
I = ( (n − 2) × 180 ) ⁄ n
We know the interior angle, so plug it in and solve for n:
160 = ( (n − 2) × 180 ) ⁄ n
160n = (n − 2) × 180
160n = 180n − 360
-20n = -360
n = 18
