You can put this solution on YOUR website! the perimeter of a rectangle is 100cm, and its diagonal has length x. express the area of the rectangle as a function of x.
Perimeter = 2(length + width) = 100 cm
length + width = 50 cm
L^2 + W^2 = x^2
length = sqrt[x^2-width^2]
width = sqrt[x^2-length^2]
Area = length*width = sqrt[(x^2-W^2)(x^2-L^2)]