Answer
Pythagorean Triple.
Work Step by Step
The Pythagorean Theorem states that for a right triangle, $a^{2} +b^{2} = c^{2}$. In order to figure out if these sides can be a Pythagorean Triple, we plug them into the Pythagorean Theorem:
$13^{2} + 84^{2} = 85^{2} \\\\ 7225=7225$
This is true, so it is a Pythagorean Triple.