atan(6*x - 1)
d --(atan(6*x - 1)) dx
6 -------------- 2 1 + (6*x - 1)
-72*(-1 + 6*x) ------------------ 2 / 2\ \1 + (-1 + 6*x) /
/ 2 \ | 4*(-1 + 6*x) | 432*|-1 + ---------------| | 2| \ 1 + (-1 + 6*x) / -------------------------- 2 / 2\ \1 + (-1 + 6*x) /