$y=\cot ^{-1} \frac{1-x}{1+x}$ হলে $\frac{d y}{d x}=$কত ?

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

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

$\frac{1}{1+x}$

$\frac{1}{1-x}$