$\frac{d}{d x}\left(\tan ^{-1} \frac{2 x}{1-x^{2}}\right)=?$

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

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

$2$

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