Like many others the Pythagorean Theorem, $ c^2 = a^2 + b^2 $, is my favorite theorem. I find it to be a very practical and useful theorem in the real world. It is a theorem not only used by people in the math field but it is used in many other fields such as construction. It seems that as math buffs we seem to be attracted to geometry, one of the funniest disciplines in math, in my opinion of course.
