if I have u = ln(root(x^2 + y^2)) then in the first partial derivative d^2u/dx^2 (or Uxx in other words) should I get 2x/root(x^2 + y^2) or -x/(x^2 + y^2)^3/2.

I need to remember what I have to do exactly and I won't ask too many questions like this as I would be spamming the boards.

Please reply soon, thanks.