2 atanh (x)
2*atanh(x) ---------- 2 1 - x
2*(1 + 2*x*atanh(x)) -------------------- 2 / 2\ \-1 + x /
/ 2 \ | 3*x 4*x *atanh(x) | 4*|- ------- - ------------- + atanh(x)| | 2 2 | \ -1 + x -1 + x / ---------------------------------------- 2 / 2\ \-1 + x /