f(x)=(a2^x-1)/(2^x+1)是R上的奇函数
f(-x)=-f(x)
[a2^(-x)-1]/[2^(-x)+1]=-(a2^x-1)/(2^x+1)
[a-2^x]/[1+2^x]=-(a2^x-1)/(2^x+1)
(a-2^x)/(2^x+1)+(a2^x-1)/(2^x+1)=0
a-2^x+a2^x-1=0
a-1+a2^x-2^x=0
(a-1)+2^x(a-1)=0
(a-1)(2^x+1)=0
a=1
f(x)=(2^x-1)/(2^x+1)=(2^x+1-2)/(2^x+1) = 1 - 2/(2^x+1)
2^x+1＞1
0＜1/(2^x+1)＜1
-2＜-2/(2^x+1)＜0
-1＜1-2/(2^x+1)＜1
值域（-1,1)