The area of a rectangle is equal to length times width in which the perimeter is equal to 2 times the sum of length and width. A circle's circumference is equal to 2pi*r. Area of circle is pi*r^2. In this case,
Rectangle A: A= lw = l*(p/2 - l)
Circle: A = pi*r^2 = pr/2
let as say r = l , then A of the circle is greater.