Answer
(k+12n)(k-7n)
Work Step by Step
You are given $k^{2}$+5kn-84$n^{2}$. Factor it out:
$k^{2}$+12kn-7kn-84$n^{2}$ -break out the middle value-
($k^{2}$+12kn)+(-7n-84$n^{2}$) -group the first two and last two terms-
k(k+12n)-7n(k+12n) -Find the GCF of each grouping-
(k+12n)(k-7n) -factor out the common term-
=(k+12n)(k-7n)
