x^2 - 9 can be factored completely as (x+3)(x-3).

<p>To factor this expression, we can use the difference of squares formula,</p><p> which tells us that a^2 - b^2 can be factored as (a + b)(a - b). In </p><p>this case, a = x and b = 3, so we have:</p><p>x^2 - 9 = (x + 3)(x - 3)</p>