atan(2*x + 1)
d --(atan(2*x + 1)) dx
2
--------------
2
1 + (2*x + 1)
-8*(1 + 2*x)
-----------------
2
/ 2\
\1 + (1 + 2*x) /
/ 2 \
| 4*(1 + 2*x) |
16*|-1 + --------------|
| 2|
\ 1 + (1 + 2*x) /
------------------------
2
/ 2\
\1 + (1 + 2*x) /