how to find the area of a pentagon?

If the pentagon is a REGULAR pentagon (i.e., all sides of the pentagon have the same size "x"), then the area of the pentagon is:

A = 1.72 * x^2

If you wanted to derive this yourself so that you better understand where the formula came from, you could divide the pentagon into 5 equal triangles, then get the area for any one of the triangles, then multiply the area of the one triangle by 5 to get the area of the pentagon.