College Algebra, Chapter 4, 4.4, Section 4.4, Problem 18

Determine all rational zeros of the polynomial $P(x) = x^3 + 4x^2 - 3x - 18$, and write the polynomial in factored form.

The leading coefficient of $P$ is $1$, so all the rational zeros are integers:

They are divisors of the constant term $-18$. Thus, the possible candidates are

$\pm 1, \pm 2, \pm 3, \pm 6, \pm 9, \pm 18$

Using Synthetic Division







We find that $1$ and $3$ are not zeros but that $2$ is a zero and that $P$ factors as

$x^3 + 4x^2 - 3x - 18 = (x - 2)(x^2 + 6x + 9)$

We now factor $x^2 + 6x + 9$ using the perfect square formula. So


$
\begin{equation}
\begin{aligned}

x^3 + 4x^2 - 3x - 18 =& (x - 2)(x + 3)^2
\\
\\
x^3 + 4x^2 - 3x - 18 =& (x - 2) (x + 3) (x + 3)

\end{aligned}
\end{equation}
$


Therefore, the zeros of $P$ are $2$ and $-3$.