Answer
It can be a right triangle.
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 the sides of a right triangle, we plug them into the Pythagorean Theorem:
$15^{2} + 36^{2} = 39^{2} \\\\ 1521=1521$
This is true, so it can be a right triangle.
