Someone recently told me that he had come up with a simple and clever way to show that the diagonal of a unit square is sqrt(2). One for the fifth grade elementary school. Here's how the method begins:
"The area of a rectangle is the side times the side. And the area of a rhombus is 1/2 * diagonal times diagonal. And a square is both a rectangle and a rhombus. (...)"
Here the description of this method breaks off. Can you complete?