x^4y-7x^2y^2+6-3xy^3-4x^3按字母x的降幂排列和按y的升幂排列,

1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) 因式分解 x-xy+3y-3x 2x+xy-y-4x+5y-6 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 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 x^3y(-4y)^2+(-7xy)^2*(-xy)-5xy^3*(-3x)^2 5x^3y*(-3y)^2+(-6xy)^2*(-xy)+xy^3*(-4x^2) 化简：x-y/x+3y÷x^-y^2/x^2+6xy+9y^2-(xy/x+y) 因式分解：x(y-3)-(2y-6) (x+y)^3-(x-y)^2(x+y) x(x^2-xy)-(4x^2-4xy) 分解公因式分解 x(y-3)-(2y-6) 2.(x+y)^3-(x-y)^2(x+y) 3.x(x^2-xy)-(4x^2-4xy) 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 诺x+y=6,xy=4 求(5x-4y-3xy)-(8x-y+2xy) 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) (x-2xy)*(-xy+2y*y)-(3x*x-2xy)(x-9xy+6y*y)答案应为-2x-x*x-3x， x+y=8,xy=-2,求(5xy+4x+7y)+(6x-3xy)-(4xy-3y)的值 x^+2xy+y^+4=16 x^-2xy+y^=16 求(3xy+6y^)+|x^-(2xy+2y^-3x^)|的值