Answer:
13
Explanation:
In a right triangle, the square of the hypotenuse (longest side, opposite the right angle) is always equal to the sum of the other two sides' squares. This is called the Pythagorean Theorem.
The square of 5 is 25 and the square of 12 is 144.
25 + 144 = 169
169 is the square of the hypotenuse, the square root of 169 is the hypotenuse: