#### Answer

$x^3-9x = (x)~(x+3)~(x-3)$

#### Work Step by Step

The general form of factoring the difference of two squares is as follows:
$x^2-y^2 = (x+y)~(x-y)$
Let's consider this trinomial: $~x^3-9x$
First we can factor by using the GCF:
$x^3-9x = (x)~(x^2-9)$
Then we can factor by using the difference of two squares.
We can factor the trinomial as follows:
$x^3-9x = (x)~(x^2-9)$
$x^3-9x = (x)~(x+3)~(x-3)$