若xy=1,x-2y=3,-6x^2y+12xy^2=多少?再加说明,

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 若x-y=4,xy=1,则(2x+y-2xy)-(3x+2y+xy)-(4xy+3y-5x)= 若x-y=4,xy=1,求(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 化简求值x-4y/2x-7xy+3y×x-2xy-3y/2x+3xy-2y÷3x-6y/4x-4xy+y,其中：x=1999,y=-1 4xy-[(x²+5xy-y²)-(3xy-1/2y)]x=3,y=-6 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=4,x-y=6,求xy(y^2+y)-y^2(xy+2x)-3xy的值. (x+y)(x-y)+(x-y)^2-(6x^2×y÷2y-2xy^2÷2y)其中x=-3,y=1/3 已知1/x=1/y=6,则3x-2xy+3y/3xy+x+y=?已知1/x+1/y=6,则3x-2xy+3y/3xy+x+y=? 若x+y=4 x-y=6 求xy(x^2+y)-y^2(xy+2x)-3xy的值求值 已知xy=-2,x-y=3,求（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y 若1/X-1/Y=3,则2X+XY-2Y/X-2XY-Y=? 若1/x-1/y=1/3,求(2x+3xy-2y)/(x-3xy-y) 若1/x+1/y=2,则(2x-xy+2y)÷(3x+5xy+3y) 若1/x-1/y=3,求(2x+3xy-2y)/(x-2xy-y)的值 若1/x -1/y =3,求(2x+3xy-2y)/(x-y-2xy) 若1/X—1/Y=2,求3X-2XY-3Y/X-2XY-Y 若1/x-1/y=3,求（2x-3xy-2y)/(x-2xy-y)的值