My favorite theorem is the Pythagorean Theorem. I like it because it is very applicable throughout geometry. A lot of theorems in math may have only a couple of areas in which they are applicable, but the Pythagorean Theorem is used in algebra to find the length of lines, and geometry. Also, it is a very easy to understand theorem and you don't need to be a "math genius' to figure out how to use and apply it
