1/(3*(-1 + x)) - (-1 + x)/(3*(1 + x + x^2))
1 -1 + x
---------- - --------------
3*(-1 + x) / 2\
3*\1 + x + x /
x
---------------------
/ 2\
(-1 + x)*\1 + x + x /
x/((-1 + x)*(1 + x + x^2))