设z=2^x，则y=f（x）=(1-z)/(1+z)反解出z=(1-y)/(1+y)那么2^x=(1-y)/(1+y)x=log以2为底[(1-y)/(1+y)]的对数反函数就是y=log以2为底[(1-x)/(1+x)]的对数
