若x\y=2\7,求7x^2-3xy+2y^2\2x^2-3xy+7y^2

求（3x^+y^-5xy）-【2x^-（-4xy-y^+7x^）】=? 求（3x^+y^-5xy）-【2x^-（-4xy-y^+7x^）】=? 已知x=3y,试求（x-y)^2+2xy-y^2/x^2+7xy+y^2 已知x=3y,试求(x-y)^2+2xy-y^2/x^2+7xy+y^2 已知xy^2=-2求xy（2x^3y^7+5x^2y 若1/x-1/y=2,求3x-2xy-3y/x-xy-y的值3x-2xy-3y/x-xy-y 不好意思，是3x-2xy-3y/x-2xy-y 已知1/x-1/y=2,求3x+7xy-3y/2x-3xy-2y答案是1/x-1/y=2(y-x)/xy=2 得：x-y=-2xy(3x+7xy-3y)/(2x-3xy-2y)=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy)=xy/(-7xy)=-1/7 谁能帮我解释一下=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy) 是怎 若x=y=6,xy=2,求2x+3y-3xy+（4xy-3x）-（4y-7）的值 若(3xy+2)^2+|7-x-y|=0,求代数式(5xy+10y)-[-5x-(4xy-2y+3x)]的值 若3x-4xy+y=-3,2x+3xy-2y=8,求5x-18xy+7y的值 若(3xy+2)+|7-x-y|=0,求代数式（5xy+10y）-[-5x-（4xy-2y+3x）]的值. 已知X/Y=2/7,求x^2-3XY+2Y^2/X^2-2XY+Y^2 已知x/y=7/2,求2x+3xy+2y/x+2xy+y的值 已知x+y=4,xy=2,求代数式2(3x+2xy)+(2xy+3x+2y)-(4xy-7y)的值 若(y-x)/xy=3,求分式(2x+3xy-2y)/(x-2xy-y)的值 若y-x/xy=3,求分式2x+3xy-2y/x-2xy-y 若x+y-5xy=0,求(2x-3xy+2y)/(x+2xy+y)的值 若xy=2（x+y),求 （3x-5xy+3y)÷(-x+3xy-y) 的值