3x^2+2xy-4y^2-(3xy-4y^2+3x^2) 急了答对给分

(-3xy+2xy)-(4xy+xy) xy-2{xy-[3x^2y-(4xy^2+0.5xy)]+4x^2y}+6xy^2 （X-3xy+4xy-y）-[-2x-2（xy-3/2xy）-y]+6xy的过程 （-3x^y+2xy)-( )=4x^+xy 化简：3x^2-[5xy-(x^y-3xy)+4x^2y-8xy] x^3y(-4y)^2+(-7xy)^2*(-xy)-5xy^3*(-3x)^2 5x^3y*(-3y)^2+(-6xy)^2*(-xy)+xy^3*(-4x^2) 3(x^2y+xy)-4(xy-2x^2y)-(-xy) 当x-y=2xy时,求4x-3xy-4y/xy XY(XY+3)+(XY+4)+4(X+Y+1)-(X+Y+2) 3（x平方y+xy)-4(xy-2x平方y)-(xy) 一道数学题(3x^2y-4xy^2)/xy 计算：5xy^2-[3xy^2-(4xy^2-2x^2y)]+2x^2y-xy^2 5xy^2-(3xy^2-(4xy^2-2x^2y))+2x^2y-xy^2求 5x^2y-3xy^2+4xy-14xy^2+4xy-2x^2y（化简） 因式分解:12xy^2(y-x)+xy^3(x-y)+4x^2y(x-y) -3(xy-2x²)-[y²-(5xy-4x²)+2xy] 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