若x+y=8,xy=7,球3xy-x-y+4的值

若x+y=8,xy=7,球3xy-x-y+4的值 |x|/x+y/|y|+xy/|xy|= 若1/x-1/y=2,求3x-2xy-3y/x-xy-y的值3x-2xy-3y/x-xy-y 不好意思，是3x-2xy-3y/x-2xy-y 若3x-4xy+y=-3,2x+3xy-2y=8,求5x-18xy+7y的值 x加y=8,xy=7,求3xy减x减y+4 x+y=8,xy=-2,求(5xy+4x+7y)+(6x-3xy)-(4xy-3y)的值 若x+y分之xy=2,则-x+3xy-y分之3x-xy+3y=多少? 若xy/x+y=2,则3x-5xy+3y/-x+3xy-y=?/是分之 若x+y分之xy=2,则-x+3xy-y分之3x-xy+3y=多少? 若xy/x+y=2,则3x-xy+3y/-x+3xy-y= 若xy=2（x+y),求 （3x-5xy+3y)÷(-x+3xy-y) 的值 诺x+y=6,xy=4 求(5x-4y-3xy)-(8x-y+2xy) 已知xy/x+y=2,求代数式8x-5xy+8y/-x+3xy-y的值 若(y-x)/xy=3,求分式(2x+3xy-2y)/(x-2xy-y)的值 若y-x/xy=3,求分式2x+3xy-2y/x-2xy-y 已知xy/x+y=3,则代数式2x-7xy+2y/-x+xy-y的值是多少? 若x+y-5xy=0,求(2x-3xy+2y)/(x+2xy+y)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