The third side is 4
So Pythagorean's theorem is the following
[tex]Short^2 + Long^2 = Hypotenuse^2[/tex]
From here we can input the following information that we know
[tex]Short^2 + \sqrt{33}^2 = 7^2\\Short^2 + 33 = 49\\Short^2 = 49 - 33\\Short^2 = 16\\Short = \sqrt{16}\\Short = 4[/tex]