$$\displaystyle\frac{d}{d x } \left(4 \log_{ e }({ { x }^{ 2 } +1 }) \right)$$
$\frac{8x}{x^{2}+1}$
$\frac{8\left(1-x^{2}\right)}{\left(x^{2}+1\right)^{2}}$
