## Algebra 1: Common Core (15th Edition)

The expression can not be factored because there are no factors of $18$ with a sum of $15$.
Attempting to factor the trinomial, we search for two factors of $ac=2\cdot 9=18$, whose sum is $b=15$ Factors of 18:$\quad 1,2,3,6,9,18$ 6 and 9 add to 15, but $6\cdot 9\neq 18.$ The expression cannot be factored because there are no factors of $18$ with a sum of $15$.