3x^2-7xy-6y^2+7x+12y-6(因式分解）,速求

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: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^2-xy-2y^2+x+7y-6 x²+xy-2y²-x+7y-6 3(x-y)²-7(x-y)+8(x-y)²+6(x-y)求详细过程（2） 5xy-4x²y-8xy²+3xy-xy²+4x²y 3/x —2/y=3 (2x-3y-xy) / (7xy+9y-6x)= x^3+x+30x^2-4xy+4y^2+7x-14y+12 x^3y(-4y)^2+(-7xy)^2*(-xy)-5xy^3*(-3x)^2 x(y-x)-y(x-y) (-3xy)*5c^2Y+6x^2(7/2xy^2-2y^2) -2x(3x-7y)+(x-y)(x^2+xy+y^2） 计算 3x^2-7xy-6y^2+7x+12y-6分解因式 已知xy/x+y=3,则代数式2x-7xy+2y/-x+xy-y的值是多少? x+y=8,xy=-2,求(5xy+4x+7y)+(6x-3xy)-(4xy-3y)的值 化简：x-y/x+3y÷x^-y^2/x^2+6xy+9y^2-(xy/x+y) 计算(x^8-x^7y+x^5y^3-x^4y^4+x^3y^5-x^y^7+y^8)(x^2+xy+y^2) 因式分解 x-xy+3y-3x 2x+xy-y-4x+5y-6