Can anyone tell me what the pythrpgrees theory is (wrong spelling)

I believe you are asking about the Pythagorean theorem? If you are, here's what it is:

In mathematics, the Pythagorean theorem, aka Pythagoras's theorem, is a fundamental relation in Euclidean geometry among the three sides of a right triangle. It says that the square of the hypotenuse (the side opposite the right angle) is equivalent to the sum of the squares of the two other sides.

The Pythagorean Theorem is what you probably mean. It is basically to solve for the sides of a triangle. The equation is a^2+b^2=c^2. Plug in at least two of the variables and you will get any side.