what's the $\frac{\partial^2{f}}{\partial{x^2}}$ of this?

Question

$$f(x,y)=\ln(x^2+y^2)$$ I just need the final answer, I have done it and I want to make sure that if I did it correctly. Thanks.

Answer 1

$$\frac{\partial^2{f}}{\partial{x^2}}=\frac{2y^2-2x^2}{(x^2+y^2)^2}$$

Answer 2

The final answer should be $\frac{2(y^2-x^2)}{(x^2+y^2)^2}$.

Answer 3

$2\frac{(y^2-x^2)}{(x^2+y^2)^2}$