# How do you factor m² + 4mn - 5n²?

$\left(m + 5 n\right) \left(m - n\right)$
$\text{the factors of - 5 which sum to + 4 are + 5 and - 1}$
$\Rightarrow {m}^{2} + 4 m n - 5 {n}^{2} = \left(m + 5 n\right) \left(m - n\right)$