a^2+b^2=c^2 So you have a right triangle, right? Let's say that the shortest side (a) is three units, and the side it makes a right angle with (b) is four units. The remaining side is called the hypotenuse, or side c. So you square three and get nine, and square four and get sixteen. Add nine and sixteen to get twenty-five. So c^2=25. What squared equals twenty-five? The answer is five. Bam. Pythagorean theorem.