Know the length of two sides of a triangle and want to know the third? With the Pythagorean theorem, a^2+b^2=c^2, it's easy! Learn how to use it with this free video geometry lesson. From Ramanujan to calculus co-creator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test).