# How do you factor by grouping c^3+3c^2-9c-27?

$f \left(c\right) = {c}^{2} \left(c + 3\right) - 9 \left(c + 3\right) = \left(c + 3\right) \left({c}^{2} - 9\right)$
$= {\left(c + 3\right)}^{2} \left(c - 3\right)$