Assuming the vertex of the triangle shown is the center of the pentagon, and the line segment shown is an altitude of the triangle:
If we join the center of (the circumscribed circle and of) the pentagon to the 5 vertices, 5 isosceles triangles are formed, all congruent to the one shown in the figure. It is clear that these triangles are congruent, so to find the area of the pentagon, we find the area of one of these triangles and multiply by 5.
The base of the triangle is 22.3 in, and the height is 15.4 ins, thus the area of the pentagon is:
