y= 1/2+1/(2^x-1) = (2^x -1 + 2)/2(2^x-1)
=(2^x+1)/2(2^x-1)
y(-x) =(2^(-x)+1)/2(2(^-x)-1)
= (1+2^x)/2(1-2^x)
= - y(x)
为奇函数