The radius is √25=5 in this case. find the area of each triangles first. (the pentagon can be divided into 5 isosceles triangles) the two equal sides are 5 each, the angle between them is 360/5=72 degree, so the base side is 2*5*sin36, and the height is 5*Cos36 the area of each triangle is (1/2)*2*5*Sin36*5*Cos36 the total area of the 5 triangles is: 5*(1/2)*2*5*Sin36*5*Cos36 use a calculator: A≈59.44
