Pythagorean theorem that only works with right triangles! People use Pythagorean theorem to find the length of the hypotenuse of a right triangle if they know the length of the other two sides (legs)!
Including that people also use the Pythagorean theorem to know whether a triangle is a right triangle!
The equation used is : a^2 + b^2 = c^2
Example :
Suppose that you have right triangle has a = 24 and b = 7
I actually just learned this in 8th grade and it was so easy its crazy but its honestly simple it helps you solve the triangles and things and the equation is a squared + b squared = c squared and the a and b you would plug in the sides of the triangle or whatever shape your working with and square those numbers then find c by adding the two and then you square the c at the end and that will be your answer.