Mathematics

Problem

y = \cot^{-1}\left(\frac{1+x}{1-x}\right)

, then

\frac{dy}{dx} =

(a)

\frac{1}{1 + x^2}

(b)

-\frac{1}{1 + x^2}

(c)

\frac{2}{1 + x^2}

(d)

-\frac{2}{1 + x^2}