You can put this solution on YOUR website! I gave your probelm directions and changed your expression a little to be what I see most often. If I guessed wrong,ley me know.
You need to multiply the denominator by its conjugate, so that it becomes the difference between two squares (a+b)(a-b)=a^2-b^2. What ever you multiply by the denominator also has to be multiplied by the numerator.
You have to foil here:
12=4*3
The square root of 4 is 2.
Happy calculating!