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