∵1/x-1/y=3∴y-x=3xy(5x+xy-5y)/(x-xy-y)=(5x-5y+xy)/(x-y-xy)=(-15xy+xy)/(-3xy-xy)=3.5∵m²+n²=4mn∴m²+n²-2mn=2mn∴(m-n)²=2mn又∵m＞n＞0∴m-n=√(2mn)∵m²+n²=4mn∴m²...请问一下， (5x-5y+xy)/(x-y-xy)=(-15xy+xy)/(-3xy-xy)是怎么推理出来的呢？∵y-x=3xy∴x-y=-3xy将x-y=-3xy代入即可