The Pythagorean Theorem says that in a right triangle each of the legs squared add up to equal the hypotenuse squared. The converse says that a triangle is a right triangle if each of the legs squared added together equal the square of the hypotenuse. For your particular problem, square the legs and add them together and they should equal the hypotenuse squared. One thing you have to know to get through this is that, no matter what, in a right triangle the hypotenuse will ALWAYS and forever be the longest length.
