you really should use brackets after the square root symbol so we know everything that is being rooted. if you look carefully, your problem looks like

when i know it's supposed to be

. in this case it is easy to see what the problem should be, but that won't always be the case. use parenthesis to clarify, it will save you and the person responding to you a lot of frustration.

Hint. Rationalize the denominator. some algebraic manipulation would be needed after this. Think: "difference of two squares"