Algebra 1: Common Core (15th Edition)

$(m-3n)(m+9n)$
List the pairs of factors of $-27$. Identify the pair that has a sum of $6$. $\left[\begin{array}{lll} \text{Factors of -27 } & \text{Sum of factors} & \\ 1\text{ and }-27 & -26 & \\ -1\text{ and }27 & 26 & \\ 3\text{ and }-9 & -6 & \\ -3\text{ and }9 & 6 & \text{...is what we need} \end{array}\right]$ $m^{2}+6mn-27n^{2}=(m-3n)(m+9n)$