1/x-1/y=(y-x)/xy=3所以y-x=3xyx-y=-3xy所以原式=[5(x-y)+3xy]/[3(x-y)-xy]=[5(-3xy)+3xy]/[3(-3xy)-xy]=-12xy/(-10xy)=6/5
6/5，半天看懂，请将分子、分母加括号
