How do i find the area of a pentagon with only the perimeter?

Unless it is a regular pentagon, you can't. If it is regular, split it into 5 congruent triangles with angles at the center = 360/5 = 72� then draw in an altitude from a side of the pentagon (which bisects the 72� angle into two 36's, and the pentagon side into two pieces each = 1/10 of the perimeter) and use tangent to get the length of the altitude . Use this to get each triangle's area then multiply by 5