Answer
$3x(x+2)(x-2)$
Work Step by Step
We factor $3x^3-12x$.
Factor out 3x to get:
$3x(x^2-4)$
The term on the right in parentheses is a difference of two squares, and can be written as:
$3x(x+2)(x-2)$
Upon further investigation, we see that it is completely factored, so the final answer is:
$3x(x+2)(x-2)$