2x^2-1xy+15y^2-3x+7y-2因式分解

1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) 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 因式分解x^2y^2+x^2y+xy^2+3xy+x+y+1 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 因式分解:12xy^2(y-x)+xy^3(x-y)+4x^2y(x-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+y-2)(x+y-2xy)+(xy-1)^2 计算3xy[2xy-x(y-2)+x-1] x²/xy-x/y 3x/4x+y - x-2y/4x+y (1-y/y+x)÷x/y²-x² (x+y)(x+y+2xy)+(xy+1)(xy-1)(x+y)(x-y)+4(y-1) X^Y-2XY^2+y^3 x²-y²+5x+3y+4（x+y-2xy)(x+y-z)+(xy-1）² x^3y(-4y)^2+(-7xy)^2*(-xy)-5xy^3*(-3x)^2 (-1/3xy)^2•[xy(2x-y)-2x(xy-y^2)] xy(xy+1)+xy+3-2(x+y+1/2)-(x+y-1)^2因式分解 (-3分之1xy)的平方×[xy(2x-y)-2x(xy-y的平方)] x-y/x+y=-1/2,x*x-xy-2y*y/x*x-3xy+2y*y的解是多少?同上,请将过程写出, XY(XY+3)+(XY+4)+4(X+Y+1)-(X+Y+2)