# How do you factor a²+4b-ab-4a?

$= \left(a - 4\right) \left(a - b\right)$
${a}^{2} + 4 b - a b - 4 a = {a}^{2} - a b - 4 a + 4 b$
$= a \left(a - b\right) - 4 \left(a - b\right)$
$= \left(a - 4\right) \left(a - b\right)$