What is pothagrum?

Answer 1

It seems like there might be a typo in your question. It's possible you are referring to the Pythagorean theorem, which states that in a right-angled triangle, the square of the length of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides. This mathematical principle is named after the ancient Greek mathematician Pythagoras.