Answer
$(x+1)(x-5)$
Work Step by Step
The given expression, $
x^2-4x-5
,$ has $c=
-5
$ and $b=
-4
.$
The possible factors of $c$ are $
\{ 1,-5 \}
,\{ -1,5 \}
$. Among these factors, the pair whose sum is equal to $b$ is $\{
1,-5
\}.$ Hence, the factored form is
\begin{array}{l}\require{cancel}
(x+1)(x-5)
.\end{array}