1、x/y=2,则上下同时除以y²得到：(x²+2xy-3y²)/(x²-xy+y²)=[(x/y)²+2(x/y)-3]/[(x/y)²-(x/y)+1]=[4+4-3]/[4-2+1]=5/3;2、(1/a)-(1/b)=2,b-a=2ab,a-b=-2ab故(2a+ab-2b)/(a-3ab-b)...