Answer: a. 144 degrees
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Work Shown:
E = exterior angle
n = number of sides
For any regular polygon, E = 360/n.
In this case, n = 10 as there are 10 sides, so E = 360/n = 360/10 = 36 degrees is the measure of each exterior angle.
Each interior angle is 180-E = 180-36 = 144 degrees
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An alternative is to plug n = 10 into the formula below to get the measure of each interior angle i
i = 180(n-2)/n
i = 180(10-2)/10
i = 180(8)/10
i = 1440/10
i = 144
note: S = 180(n-2) is the sum of all the interior angles of any convex polygon. Dividing this sum over n will evenly divide the angle total to each interior angle.