Answer
$$\left(a^2+3\right)\left(a+2\right)\left(a-2\right)$$
Work Step by Step
Factoring the expression completely, we find:
$$ \left(a^2+3\right)\left(a^2-4\right) $$
We recognize the difference of two squares:
$$\left(a^2+3\right)\left(a+2\right)\left(a-2\right)$$
