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