Question

当x-y/x+y=2时，代数式x-y/x+y-2x+2y/x-y的值是

Answer 1

原题加不加括号？
这是加括号的解
（x-y）/(x+y)=2时，代数式(x-y)/(x+y)-(2x+2y)/(x-y)
解：x-y=2(x+y)
原式=(x-y)/(x+y)-2(x+y)/(x-y)
=2-(x-y)/(x-y)
=2-1
=1

Answer 2

∵(x-y)/(x+y)=2
∴（x+y)/(x-y)=1/2
∴（2x+2y)/(x-y)=2（x+y)/(x-y)=2×1/2=1
原式=2-1=1

Answer 3

∵x-y/x+y=2
∴x+y/x-y=1/2
∴x-y/x+y-2x+2y/x-y=2-2*1/2=2-1=1

Answer 4

∵x-y/x+y=2∴x-y=2（x+y）∴

∴x-y/x+y-2x+2y/x-y=x-y/x+y-2(x+y/x-y)
=2-2×1/2
=2-1
=1