49x^4+4y^4/7x^3y+2xy^3,其中7x=2y

因式分解:12xy^2(y-x)+xy^3(x-y)+4x^2y(x-y) x^3y(-4y)^2+(-7xy)^2*(-xy)-5xy^3*(-3x)^2 因式分解 x-xy+3y-3x 2x+xy-y-4x+5y-6 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) 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 求（3x^+y^-5xy）-【2x^-（-4xy-y^+7x^）】=? 求（3x^+y^-5xy）-【2x^-（-4xy-y^+7x^）】=? 化简：3x^2-[5xy-(x^y-3xy)+4x^2y-8xy] 化简2(x²y+xy)-3(x²y-xy)-4x²y 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 （-3x^y+2xy)-( )=4x^+xy x²/xy-x/y 3x/4x+y - x-2y/4x+y (1-y/y+x)÷x/y²-x² 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+y)(x+y+2xy)+(xy+1)(xy-1)(x+y)(x-y)+4(y-1) 已知x-y=8 xy=7,则3xy-2x+2y+4(y-x)²=? x²-y²+5x+3y+4（x+y-2xy)(x+y-z)+(xy-1）² x^3+x+30x^2-4xy+4y^2+7x-14y+12 计算:2xy/(x+y)².(x+y)/4y