If `f(x)=log((1+x)/(1-x))a n dg(x)=((3x+x^3)/(1+3x^2))` , then `f(g(x))` is equal to (a)`f(3x)` (b) `{f(x)}^3` (c) `3f(x)` (d) `-f(x)`

Explanation

To solve the problem, we need to find \( f(g(x)) \) where \( f(x) = \log\left(\frac{1+x}{1-x}\right) \) and \( g(x) = \frac{3x + x^3}{1 + 3x^2} \).

### Step-by-step Solution:

1. **Substitute \( g(x) \) into \( f(x) \)**:
\[ f(g(x)) = f\left(\frac{3x + x^3}{1 + 3x^2}\right) = \log\left(\frac{1 + g(x)}{1 - g(x)}\right) \]
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