$$\displaystyle\frac{d}{d x } \left( \ln ( \sqrt{ \frac{ 1- { x }^{ 2 } }{ 1+ { x }^{ 2 } } } ) \right)$$
$-\frac{2x}{1-x^{4}}$
$\frac{2\left(-3x^{4}-1\right)}{\left(1-x^{4}\right)^{2}}$
