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 `f(3x)` (b) `{f(x)}^3` (c) `3f(x)` (d) `-f(x)`

Explanation

To solve the problem, we need to find \( f(g(x)) \) given the functions:

1. \( f(x) = \log\left(\frac{1+x}{1-x}\right) \)
2. \( g(x) = \frac{3x + x^3}{1 + 3x^2} \)

### Step-by-Step Solution:

**Step 1: Substitute \( g(x) \) into \( f(x) \)**
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