atan(3*x)
d --(atan(3*x)) dx
-54*x
-----------
2
/ 2\
\1 + 9*x /
/ 2 \
| 36*x |
54*|-1 + --------|
| 2|
\ 1 + 9*x /
------------------
2
/ 2\
\1 + 9*x /