#### Answer

$(x-6)(x+3)$

#### Work Step by Step

The leading coefficient is 1 so the trinomial can be factored by looking for the factors of the third term whose sum is equal to the coefficient of the middle term.
Note that $-18 = -6(3)$ and $-6 + 3 = -3$.
Thus, the factors of the the trinomial are $x-6$ and $x+3$.
Therefore,
$x^2-3x-18=(x-6)(x+3)$.