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) /