1/(2^-x-1)=2^x/(1-2^x)
所以f(x)-f(-x)=x[1/(2^x-1)+1/2]+x[2^x/(1-2^x)+1/2]
=x[1/(2^x-1)+2^x/(1-2^x)+1]
=x[1/(2^x-1)-2^x/(2^x-1)+1]
=x[/(2^x-1)-2^x/(2^x-1)+1]
=x*{(1-2^x+2^x-1)/(2^x-1)]
=0
f(x)=f(-x)
偶函数