Can area of rectangle be greater than the square of its diagonal? 
Q: A wall, rectangular in shape, has a perimeter of 72 m. If the length of its diagonal is 18 m, what is the area of the wall ?

The answer given to me is area of 486 m2. This is the explanation given to me



Is it possible to have a rectangle of diagonal 18 m and area greater than the area of a square of side 18 m ?

No. Using Pythagoras and a simple inequality we get
$$d^2=a^2+b^2\geq 2ab\geq ab$$
If $a,b$ are the sides and $d$ the diagonal
