Maureen M. answered 03/23/19
Math tutor experienced in geometry, Algebra II and pre-calculus
The hypotenuse of a right triangle is the the square root of the sum of the squares of the bases. This is often written as c2 = a2 + b2, where c is the hypotenuse and a and b are the bases.
So for this example c2 = 52 + 122 = 25 +144 = 169.
c is the square root of 169, which is 13.