If y=\cos^{-1}( \frac{2x}{1+x^{2}}) then \frac{dy}{dx} is equal to [NDA II 2017]

Correct Answer is : −21+x2 for all |x|<1

- \frac{2}{1+x^{2}} for all |x|<1

- \frac{2}{1+x^{2}} for all |x|>1