[SOLVED] Some help with limits

I have to evaluate the following limits:

a) lim x -> 7

(square root(x+2)) -3 / (x-7

I was unable to solve this

b) lim x -> 0

1/x - 1/(x^2 + x)

Somehow simplified it to 0 / x+1... this makes no sense.

c) lim x -> -infinity

(square root(4x^2 + 1)) / (3x-5)

I somehow got denominator 0 and was unable to solve.

What I did was take the x^2 out of the square root on top and got:

x^2 square root(4+1/x^2) / 3/x - 5/x^2

I am pretty sure the denominators go to zero and and this point I'm lost.

Please help. I can do this and have done similar problems before, just need a little kick start.