/ 3\ | -1 + x | 6*|1 - -------| | 3 | \ x / --------------- x
3 6 - 6*x 6 + -------- 3 x ------------ x
/ 3\ 6*\-1 + x / 6 - ----------- 3 x --------------- x
/ 3\ 6*\1 - x / 6 + ---------- 3 x -------------- x
6.0*(1.0 - (-1.0 + x^3)/x^3)/x
3 -1 + x 6 - 6*------- 3 x ------------- x