My favorite theorem is the Pythagorean Theorem
The square of the hypotenuse of a right triangle is equal to the sum of the squares on the other two sides.
$ a^2 + b^2 = c^2 $
I like this theorem because it is a simple theorem that I learned in 9th grade but still use it today.
I also see that it is sarah's fovorite theorem as well, I we can chalk 2 up for old Pythagoras
