How do you differentiate $\displaystyle \sqrt{\left ( \frac{1-x}{1+x}\right )}$ with respect to x?

I've tried using $\displaystyle \frac{dy}{du}\times \frac{du}{dx}$ with $\displaystyle u=\left ( \frac{1-x}{1+x}\right )$ and $\displaystyle u=(1-x)(1+x)^{-1}$ but neither seems to get the right answer.