x^2-xy-2y^2+x+7y-6

1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) x^2-xy-2y^2+x+7y-6 x²+xy-2y²-x+7y-6 化简：x-y/x+3y÷x^-y^2/x^2+6xy+9y^2-(xy/x+y) 因式分解 x-xy+3y-3x 2x+xy-y-4x+5y-6 (-x-y)(x^2+xy+y^2) 已知X+y=6,xy=7 求x^2y+xy^2=已知X+y=6,xy=7 x^2y+xy^2 化简x^-y^/x^-2xy+y^ 2*(x-y)²(y-x)(xy) 因式分解:8(x-2y)-x(7x+y)+xy. 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^2+xy/x-y)/（xy/x-y)计算 (x-2xy)*(-xy+2y*y)-(3x*x-2xy)(x-9xy+6y*y)答案应为-2x-x*x-3x， x^2-xy-6y^2+3xy+y+2 3y/x*x-y*y+x/x*x-2xy+y*y+6y*y/x*x*x-x*x*y-xy*y+y*y*y等于多少? 6（x-y)-7(xy)=21,2(x-y)-5(x+y)=-1 X-Y/2X+2Y XY/X+Y² 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