Answer
$\left\{-7, -4\right\}$
Work Step by Step
Write the equation in the form $ax^2+bx+c=0$ to obtain:
$$x^2+11x+28=0$$
Recall:
If the trinomial $x^2+bx+c$ is factoable, then its factored form is $(x+d)(x+e)$ where $c=de$ and $b=d+e$.
Look for factors of $28$ whose sum is equal to $11$.
Note that $28=7(4)$ and $11=7+4$.
Thus, $d=7$ and $e=4$.
Hence,
$$x^2+11x+28=(x+7)(x+4)$$
The given equation is equivalent to $(x+7)(x+4)=0$.
Use the Zero-Product Property by equating each factor to zero, then solving each equation to obtain:
\begin{align*}
x+7&=0 &\text{or}& &x+4=0\\
x&=-7 &\text{or}& &x=-4\\
\end{align*}
