Bill had a garden in the shape of a right triangle. One side measured 5 yards and the other side measured 12 yards. How long was the third side - the side opposite the corner?
x^2 = 5^2 + 12^2
You can save yourself some calculation by learning a few of the basic Pythagorean triples, such as
3-4-5, 5-12-13, 8-15-17, 7-24-25
and their multiples.