x★y=xy-1,则(2★3)★(-4)等于多少

若x-y=4,xy=1,则(2x+y-2xy)-(3x+2y+xy)-(4xy+3y-5x)= x★y=xy-1,则(2★3)★(-4)等于多少 已知2/x-1/y=3,则(2y-x+4xy)/(3x-6y-5xy)=? 已知1/X-1/Y=5 ,则x-2xy-y/4x+3xy-4y 已知xy/x+y=1/2,则代数式3x-5xy+3y/-x+3xy-y= 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 若x-y=4,xy=1,求(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 (-2xy+2x+5y)-(3xy+2y-2x)-(x+4y+xy)其中x-y=4xy=-1 x-y=1,xy=2.求：(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 .已知:x-y=1,xy=-2.求:(-2xy+2 x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 xy=4 x-y=-7.5 则3（xy-2/3y)-1/2(2x=4xy)-(-2x-y) 4xy-[(x²+5xy-y²)-(3xy-1/2y)]x=3,y=-6 已知x²-3xy+4x=3,y²+xy-4y+7=0,则xy-1/2(x²+y²)的值为 已知x+y=5,xy=-1,则（3x-4y+2xy）-（2x-5y+5xy）=? 已知x+y=5,xy=-1,则（3x-4y+2xy)-(2x-5y+5xy)=_______ 已知x y=1,xy=-3,求2xy-4x 4(y-2(xy-x)) 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 （-3x^y+2xy)-( )=4x^+xy