Źródło TeX:

f^{\prime\prime}(x)=\left(\frac{1-2x^2}{1+x^2}\right)^\prime=\frac{\left(1-2x^2\right)^\prime\cdot \left(1+x^2\right)-\left(1-2x^2\right)\cdot \left(1+x^2\right)^\prime}{\left(1+x^2\right)^2}=\frac{-4x\left(1+x^2\right)-2x\left(1-2x^2\right)}{\left(1+x^2\right)^2}