Answer by
Gael (5)
For every polygon A = 0.5 * P * a (where A= area, P = perimeter, a = apothem)
For a regular pentagon with side length x this is: A = 0.5 * 5x * 0.5*x*tan(54 deg)
Which results in 1.25 * x^2 * tan(54 deg), which is approximately 1,72 * x^2.