Answer
$$(a-6)(a-2)$$
Work Step by Step
Factor
$$a^{2}-8a+12.:$$
Find numbers that are factors of $12$ and sum to $-8$
$$(-6)(-2)=12;\space -6-2=-8.$$
The polynomial is a product of two binomials:
$$a^{2}-8a+12=(a-6)(a-2).$$
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