7x^2-3y+xy-21x

(14x^3*y-7x^2*y^2+21xy^3)/(-7xy) 计算 (21xy^3-7x^2y^2+28x^3y)÷(-7xy) 7x^2-3y+xy-21x 因式分解7x^2-3y+xy-21x 分解因式7x^2-3y+xy-21x 1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) x^3y(-4y)^2+(-7xy)^2*(-xy)-5xy^3*(-3x)^2 已知xy/x+y=3,则代数式2x-7xy+2y/-x+xy-y的值是多少? 求（3x^+y^-5xy）-【2x^-（-4xy-y^+7x^）】=? 求（3x^+y^-5xy）-【2x^-（-4xy-y^+7x^）】=? （ ）+x^2-xy+2y^2=2x^2+xy+3y^23x^2+xy-7y^2-( )=x^2-2xy+y^2 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 分解因式:14x^2(x+y)-21(x+y)^2-7xy(x+y) 因式分解:12xy^2(y-x)+xy^3(x-y)+4x^2y(x-y) -2x(3x-7y)+(x-y)(x^2+xy+y^2） 计算 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 (x-2xy)*(-xy+2y*y)-(3x*x-2xy)(x-9xy+6y*y)答案应为-2x-x*x-3x， 2x²y-3(2xy-xy)-xy