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) /