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

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

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

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

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