(-3xy-7y)+[4x-3(xy+y-2x)],其中xy=-2,x-y=3,先化简,再求值.

x^3y(-4y)^2+(-7xy)^2*(-xy)-5xy^3*(-3x)^2 【x(xy-xy)-y(x-xy)】÷3xy -x-3xy+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 （X-3xy+4xy-y）-[-2x-2（xy-3/2xy）-y]+6xy的过程 xy-2{xy-[3x^2y-(4xy^2+0.5xy)]+4x^2y}+6xy^2 化简：3x^2-[5xy-(x^y-3xy)+4x^2y-8xy] 因式分解:12xy^2(y-x)+xy^3(x-y)+4x^2y(x-y) 3xy+xy+3+4xy-7化简,已知x=5,y=6 求（3x^+y^-5xy）-【2x^-（-4xy-y^+7x^）】=? 求（3x^+y^-5xy）-【2x^-（-4xy-y^+7x^）】=? （-3x^y+2xy)-( )=4x^+xy 5x^3y*(-3y)^2+(-6xy)^2*(-xy)+xy^3*(-4x^2) 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) 3(x^2y+xy)-4(xy-2x^2y)-(-xy) x-y=3,xy=5,求代数式（7xy+4x-7y）+(6x-3xy)-(3y+4xy)的值快