I'm really having trouble with this question...

When I solve it I find the answer to just be zero but apparently the answer is two or -2.

Find lim $\displaystyle 1/(((x^2+x)^1/2)+x)$

x-> - infinity

Could somebody please explain to me how to do this type of question. I understand what to do when there are variables on the top, but since there is only a one I'm very confused.