This is Section $2\mathrm{.}8$ Problem $12$:

Find the functions $f(u)$ and $g(x)$ for $y=ln(3x^2+1),$ so that $y=f(u)$ and $u=g(x)$ :

$f(u)=$

$g(x)=$

$$

Hint: The variable in the first answer is $u.$