$$- \frac{a}{x^{2} + 1}$$
2*a*x
---------
2
/ 2\
\1 + x /
$$\frac{2 a x}{\left(x^{2} + 1\right)^{2}}$$
/ 2 \
| 4*x |
-2*a*|-1 + ------|
| 2|
\ 1 + x /
------------------
2
/ 2\
\1 + x /
$$- \frac{2 a \left(\frac{4 x^{2}}{x^{2} + 1} - 1\right)}{\left(x^{2} + 1\right)^{2}}$$