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