1) Never wrote "1/0" again. It doesn't mean anything.
2) Your problem is the sign. When you square under the radical, it is not the same.
At least two ways to proceed.
a) Do you know l'Hospital? That will help.
b) (-x)^2 = x^2. See if you can figure out why changing the sign on the radical, when moving the x^2 inside, is the right thing to do.