f(x)=(2-x)/(x+b) =y
∵f(x)的图象与其反函数的图象重合
2-x=xy+by (1+x)y=2-by
1+x=(2-by)/y x=(2-by)/y -1
反函数y=（2-bx）/x -1 =(2-bx-x)/x=(2-x)/(x+b)
所以b=0
f(x)=(2-x)/x