The formula for Pythagorean Theorem is 'a' squared + 'b' squared = 'c' squared. So let's call the base of this triangle, which is 3, 'a' and the length, which is the hypotenuses, 'c'. Now we need to plug it in. So, we square 3 and square 13. It's now (9+b=169). Solve the equation and you get b^2=160. So now we solve for the square root. And the answer is 12.6491106407 which you can round to 12.65
