一、
(6x+1)/(x^2-x+3)
(4x-3)/(-x^2+x-3)=(3-4x)/(x^2-x+3)
二、
3x/[(x-1)(x-2)]=3x/(x^2-3x+2)
(3+x)/[(x-1)(2-x)]=-(x+3)/(x^2-3x+2)