Implicit Differation and Chain Rule

First, I really need help with implicit differentiation. I tried reading in my book, but they use very basic problems and I did not find it helpful.

The problem I need help with is:

x^2 + xy - y^2 = 4 Solver for y'

I can not get the correct answer. I got (2x)/(x-2y)=y' (This is incorrect).

Next I need help with the chain rule. I understand how to do this, but I am having problems with one question. The question is:

Sqrt (2x)/(x^2+1.8)) <- For this problem, everything is under the radical.

Thank you!!!