x^2+xy=2 y^2+xy=7,则2（x-y)(x+y)=

已知xy/x+y=3,则代数式2x-7xy+2y/-x+xy-y的值是多少? 已知x+y=1,xy=-2,则x²y+xy²-2xy x*x+xy=3,xy+y*y=2,则x*x+2xy+y*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 |x-2|+|y-2|=0,求xy=?；|x|=-|y-7|,则xy=? 如果x+y=0,xy=-7,则x^2y+xy^2=? 如果X+Y=10 XY=7则X~2Y+XY~2=? （-3x^y+2xy)-( )=4x^+xy (XY-X^2)除以X-Y/XY=? 已知x-xy=10,xy-y=2,则x-y=（ ）,-2xy+x+y=（ ）. 已知x-y=3xy,则2x+3xy-2y除以x-2xy-y=? 已知x+xy+y=3,则(3x+2xy+3y)/(2x+xy+2y)= 已知x-y=3xy,则2x+3xy-2y/x-2xy-y= 已知x-xy=20,xy-y=-10,则x-y=( ),x+y-2xy=( ). 已知x-xy=20,xy-y=12,则x-y= ,-2xy+x+y= 已知x-xy=20 xy-y=12,则x-y=（ ）,x+y-2xy=（ ）. 已知:x-xy=20,xy-y=12,则x-y=...,-2xy+x+y=... 已知x-xy=20,xy-y=-10,则x-y=?,x+y-2xy?