Answer
$2(a-2)(a-7)$
Work Step by Step
Factor out the common factor of 2, then factor the resulting binomial.
$2a^2-18a+28=2(a^2-9+14)$
The first term in each binomial must be a, since $a^2$ has no coefficient.
The operation in each binomial must be subtraction, since the trinomial has a positive and a negative term.
$-2+(-7)=-14$ and $-2\times(-7)=14$, so the other two terms are -2 and -7.
