The Pythagorean theorem is the idea that the sum of the two legs which are both squared is equal to the hypotenuse's length squared.
*<em>look at the image I attached for a better explanation</em>
By looking at the picture, we are missing the leg's length, and by using the Pythagorean theorem, we get the equation
Thus the <u>missing side length is 12 cm</u>
Hope that helps!