Question

Find the area of the regular 20​-gon with radius 77 mm.

Answer 1

The area of a polygon equals
area = circumradius² * number of sides * sin (360 / # of sides) / 2
area = 77² * 20 * sin (360 / 20) / 2
area = 77² * 20 * sin (18) / 2
area = 118,580 * 0.30902 / 2
area = 36,643.59 / 2
area = 18,321.8 square millimeters