Given f(x) = ((1+x)/(1-x)).

Step 1: Show that $f(x)$ is an odd function.
A function $f(x)$ is odd if $f(-x) = -f(x)$.
Given $f(x) = \ln\left(\frac{1+x}{1-x}\right)$.
Substitute $-x$ into the function:

$$f(-x) = \ln\left(\frac{1+(-x)}{1-(-x)}\right) = \ln\left(\frac{1-x}{1+x}\right)$$

Using the logarithm property $\ln\left(\frac{a}{b}\right) = -\ln\left(\frac{b}{a}\right)$:

$$$$