To solve, use the Pythagorean Theorem, which says c² = a² + b². Enter 84 as a and 13 as b and square them both. This will give you 7056 for a, and 169 as b. Add them to get 7225. So, c² = 7225. Find the square root of this to get 85. So, the third side is 85 in length.
