已知x+xy=-2,xy-y=-6求代数式2x｛-4y-3[（x+xy）²+x]-½[（y-xy）²-2y]的值

已知:x+y=1,xy= -6,求代数试(5xy+2x-3y)-(-2xy)-5x的值 已知多项式-y²+14xy+A=7x²+4xy-2y²,求代数项A 当x=3,y=3分之1时,求代数出3xy-[2xy-2(xy-2分之3xy)+xy]+3xy的值 一道math题已知x²+xy=12,xy+y²=15,求代数（x+y）²-2y（x+y）的值. 已知xy除以x+y=2,求代数3x-5y+3y除以-x+3xy-y的值?123456 已知X+y=6,xy=7 求x^2y+xy^2=已知X+y=6,xy=7 x^2y+xy^2 已知xy/x+y=6,求3x-2xy+3y/-x+3xy-y的值. 已知(xy)/(x+y)=6求(3x-2xy+3y)/(-x+3xy-y)的值. 已知:x/y=-2,求x^2-2xy-3y^2/x^-6xy 已知x-xy=8,xy-y=-9,求x+y-2xy的值 已知x/y=2,求 [x^2-xy+3xy^2 ] / [ x^2+xy+6y^2]的值 已知x+y=6,xy=4,求x^2y+xy^2的值~ 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 已知xy^2=-2,求-xy（x^2y^5-xy^3-y)的值. 已知xy^2=-2 求-xy(x^2y^5-xy^3-y) 已知x+y=4,xy=-2,求代数式3(xy+2y)-(xy-6x)的值 已知x+y=4,xy=-2,求代数式3（xy+2y）-（xy-6x） 已知x^2-xy=5,xy-y^2=-3求3(x^2-xy)-xy+y^2