The perimeter of a rectangle is $40,$ and the length of one of its diagonals is $10 \sqrt{2}.$ Find the area of the rectangle.
√200=10√2, so a2+b2=200
Assuming that a and b are both integer side lengths, 102+102=200, so the sides are 10 and 10.
10 times 10 is 100, so the area of the rectangle is 100