# How do you factor 28a^3b^4+20a^2b^2-16ab^3?

$= 4 \times \left(7 {a}^{3} {b}^{4} + 5 {a}^{2} {b}^{2} - 4 a {b}^{3}\right)$
From every term we can take out $a {b}^{2}$
$= 4 a {b}^{2} \left(7 {a}^{2} {b}^{2} + 5 a - 4 b\right)$