注:分子/分母
(1/x-3)+(1/9-x^2)-(x-1/6-2x)
通分:=2(x+3)/2(x+3)(x-3)+12/2(9-x^2)-(x-1)(3+x)/2(3-x)(3+x)
=2x+6/2(x^-9)-12/2(x^-9)+(x-1)(3+x)/2(x^-9)
=2x+6-12+2x+x^2-3/2(x^-9)
=4x+x^2-9/2(x^-9)