函数的定义域是R
f(-x)=(2^(-x)-1)/(2^(-x)+1)
=(1-2^x)/(1+2^x)
=-(2^x-1)/(2^x+1)
=-f(x) 奇函数
任取 X1 、X2 且 X1 <X2
f(X1)-f(X2)=(2^X1-1)/(2^X1+1) - (2^X2-1)/(2^X2+1)
=2*(2^X1-2^X2)/[(2^X1+1)(2^X2+1)]
=2*2^X2(2^(X1-X2)-1) /[(2^X1+1)(2^X2+1)]
<0
即 f(X1)<f(X2) 函数单调递增