How do you find the definition of f(x)=x (sq. root(x+1))
I'm sure you got stuck here. The thing we need to do now is multiply by the conjugate of the numerator:
This simplifies to
Expand out the numerator, and try to cancel out as many terms as you can. Then a common factor of h should appear in all the numerator terms. Pull it out, and it should then cancel out with the h term in the denominator. Then evaluate the limit.
Can you try to take it from here?