已知:x-y=7,xy=5,则3xy-7x-7y=?

已知x-y=3xy,且xy不等于0,则-3x+6xy+3y/(7x-5y)-9xy-(3x-y) 已知:x-y=7,xy=5,则3xy-7x-7y=? 已知x-y=5,xy=3,则3xy-7x+7y=? 3xy+xy+3+4xy-7化简,已知x=5,y=6 已知xy/x+y=3,则代数式2x-7xy+2y/-x+xy-y的值是多少? 已知xy^2=-2求xy（2x^3y^7+5x^2y 已知X+Y=6,xy=3求代数式（5XY+4X+7Y)+(6X-3XY)-(4XY-3Y)的值 已知x+y=3,xy=1,求代数式5xy+4x+7y+6x-3xy-4xy+3y的值. 已知x-y=4,xy=7,则代数式(4x-5y+3xy)-(3x-4y)+7xy的值是? 已知x-y=5,xy=3,则3xy-7x+7x=____________a 抱歉已知x-y=5，xy=3，则3xy-7x+7y=____________ 已知xy/x+y=1/2,则代数式3x-5xy+3y/-x+3xy-y= 已知A=8x^2y-6xy^2-3xy,B=7xy^2-2xy+5x^2y求A-B 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x+y=2xy,且xy不等于0,则求-2x+6xy-2y/(7x+5y)-9xy-(3x+y)=___ 已知x-y=8 xy=7,则3xy-2x+2y+4(y-x)²=? 已知xy的2次方=-3,则-xy（X的2次方*y的5次方-xy*xy*xy-y)= 已知xy平方=-2,求-xy(x^3y^7-3x^3y^7-y)刚刚发现打错题了，应该是：已知xy平方=-2,求-xy(x^3y^7-3x^2y^5-y) 已知x+xy=-3,xy+y=7,试求x+2Xy+y的值