已知x+y分之xy=3,求-x+3xy-y分之2x-3xy+2y的值
问题描述：
已知x+y分之xy=3,求-x+3xy-y分之2x-3xy+2y的值
答
踩一脚就走了
答
令X+Y=M XY=N 所以XY=3(X+Y) 即 N=3M 分母上-x+3xy-y=-(x+y)+3xy=-m+3n
分子上2x-3xy+2y=2(x+y)-3xy=2m-3n 2m-3n/-m+3n=2m-9m/-m+9m=-7/8
答
由x+y分之xy=3可得 x+y=xy/3 代入（2x-3xy+2y）/(-x+3xy-y)得
（2x-3xy+2y）/(-x+3xy-y)=[-3xy+2（x+y）]/[3xy-（x+y)]=-7/8
答
xy/x+y=3
xy=3(x+y)
2x-3xy+2y/-x+3xy-y
=2(x+y)-3xy/-(x+y)+3xy
=-(x+y)/2(x+y+
=-1/2
答
x+y分之xy=3,
xy/(x+y)=3,
xy=3(x+y)
-x+3xy-y分之2x-3xy+2y
=(2x-3xy+2y)/(-x+3xy-y)
=[2x-9(x+y)+2y]/[-x+9(x+y)-y]
=-7(x+y)/8(x+y)
=-7/8