-9m²n+36mn-3n
=-3n(3m²-12m+1)再问两题~，是化简分式：（1）1/2x-1/3y分之1/2x+1/3y（2）1/x²-1/y²分之1/x-1/y谢谢~（1）(1/2x+1/3y)/(1/2x-1/3y)通分=(3y+2x)/(3y-2x)（2）(1/x-1/y)/1/x²-1/y²=(1/x-1/y)/(1/x-1/y)(1/x+1/y)=1/(1/x+1/y)=xy/(x+y)