Answer
$(x+5)(x-1)$
Work Step by Step
The two numbers whose product is $ac=
1(-5)=-5
$ and whose sum is $b=
4
$ are $\{
5,-1
\}$. Using these two numbers to decompose the middle term, then the factored form of the expression, $
x^2+4x-5
$, is
\begin{array}{l}\require{cancel}
x^2+5x-x-5
\\\\=
(x^2+5x)-(x+5)
\\\\=
x(x+5)-(x+5)
\\\\=
(x+5)(x-1)
.\end{array}
