A ladder leans against a wall four feet above the ground. The base of the ladder is three feet from the wall. How long is the ladder?
Use the Pythagorean theorem:
a^2 + b^2 = c^2
4^2 + 3^2 = c^2
16 + 9 = c^2
25 = c^2
5 = c
a^2 + b^2 = c^2
4^2 + 3^2 = c^2
16 + 9 = c^2
25 = c^2
5 = c