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