奇函数,f(x) = -f(-x)
log a(1+mx)/(x-1) = -log a(1- mx)/(-x-1)
= -log a(mx - 1)/(x + 1)
= log a (x + 1)/（mx - 1)
所以 (1+mx)/(x-1) =(x + 1)/（mx - 1)
所以 m = 1