Because the number you provided is negative, we won't get a real answer instead a complex answer.
Now simplify the square root.
To simplify a square root, find two factors where one of the factors is a perfect square.
[tex]\sqrt{-108} = \sqrt{(-3)(36)} = \sqrt{-3}\sqrt{36} = 6\sqrt{(-1)(3)} = 6\sqrt{(-1)}\sqrt{3} = 6i\sqrt{3}[/tex]
