#### Answer

$$(x + 3)(x - 1)(x + 1)$$

#### Work Step by Step

To factor this expression, we can group terms together so we can factor out a common factor:
$$(x^3 - x) + (3x^2 - 3)$$
For the first group, we can factor out an $x$ whereas for the second group, we will factor out a $3$:
$$x(x^2 - 1) + 3(x^2 - 1)$$
We can now factor the $x^2 - 1$.
$$(x + 3)(x^2 - 1)$$
The second factor can be factored even more as it is the difference of two squares, which follow the form:
$$(A - B)(A + B)$$
where $A$ is the $\sqrt x^2$ and $B$ is the $\sqrt 1$:
So now we have:
$$(x + 3)(x - 1)(x + 1)$$