## College Algebra (11th Edition)

(3 - r)(9 + 3r + $r^{2}$)
27 - $r^{3}$ is a difference of cubes, so we write it as a difference of cubes and factor: $3^{3}$ - $r^{3}$ (3 - r)($3^{2}$ + 3r + $r^{2}$) = (3 - r)(9 + 3r + $r^{2}$)