## Elementary Algebra

The solution set is $\left\{3, 6\right\}$.
Factor the trinomial by looking for the factors of 18 whose sum is equal to the coefficient of the middle term (-9). These factors are $-6$ and $-3$. This means that the factored form of the trinomial is $(x-6)(x-3)$. Thus, $x^2-9x-18=0 \\(x-6)(x-3)=0$ Equate each factor to 0 then solve each equation to obtain: $x-6=0 \text{ or } x-3=0 \\x=6 \text{ or } x=3$ The solution set is $\left\{3, 6\right\}$.