Question

What is the area of a pentagon using the side length of 4

Answer 1

In this equation, n = # of sides
Area = n * (side length)² / 4*tan (180 / n)
Area = 5 * 4² / 4 * tan (36)
Area = 80 / 4 * 0.72654
Area = 80 / 2.90616
Area =  27.5277341922

Source:
http://www.1728.org/polygon.htm