7x^2y-[xy+4(xy^2+1/8xy)-3x^2y]答对给分

7x^2y-[xy+4(xy^2+1/8xy)-3x^2y]答对给分 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 化简：3x^2-[5xy-(x^y-3xy)+4x^2y-8xy] x^3y(-4y)^2+(-7xy)^2*(-xy)-5xy^3*(-3x)^2 XY(XY+3)+(XY+4)+4(X+Y+1)-(X+Y+2) 1-2/x+y=xy,4y+6x=xy.求xy的解? x+y=8,xy=-2,求(5xy+4x+7y)+(6x-3xy)-(4xy-3y)的值 因式分解：x-4xy-2xy+8y等于? 因式分解xy(xy+2)+6(xy+8)-4(x+y-2)^2-16(x+y+1)谢谢 (x+y)(x+y+2xy)+(xy+1)(xy-1)(x+y)(x-y)+4(y-1) (x^2+2xy+y^2-4xy)*(x^2-2xy+y^2+4xy) 已知1/x - 1/y = 2,求3x+7xy-3y / 2x-3xy-2y的值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)=-1/71/x-1/y=2到(y-x)/xy=2 是怎么变化的.. (1).x^2-8xy+7y^2(2).4x^2+9xy+2y^2(3).2x^2+7xy+3y^2(4).6x^2+xy-2y^2 [(2xy^3)^2÷(3x)]·[8xy÷(4xy)],其中x=1000,y=-1 [(2xy的立方)整体的平方/(3x)]*[8xy/4xy]其中x=1000,y=-1 .(x+y-2)(x+y-2xy)+(xy-1)^2 联立方程 x^2-xy-2y^2=8(1) xy+y^2=4(2) 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