已知x+y=6 xy=8求x+2xy+y分之2x-xy+2y的值

已知x-xy=8,xy-y=-9,求x+y-2xy的值 已知xy/x+y=2,求代数式8x-5xy+8y/-x+3xy-y的值 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=6,xy=7 求x^2y+xy^2=已知X+y=6,xy=7 x^2y+xy^2 已知:x/y=-2,求x^2-2xy-3y^2/x^-6xy 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~ 诺x+y=6,xy=4 求(5x-4y-3xy)-(8x-y+2xy) 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A=8x^2y-6xy^2-3xy,B=7xy^2-2xy+5x^2y求A-B 已知X+Y=6,XY=4,求（5X-4Y-3XY）-（8X-Y=2XY）的值 已知x+y=6 xy=8求x+2xy+y分之2x-xy+2y的值 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=6,XY=-4,求（5X-4Y-3XY）-（8X-Y+2XY）的值 已知2x+xy=10,3y+2xy=6.求4x+8xy+9y=? 已知x^+xy=-5,xy+y^=8,求2x^-xy-3y^的值都是2次