Answer
$(k+8)(k-8)$
Work Step by Step
$k^{2}-64=$
...rewrite $64$ as a square.
$=k^{2}-8^{2}$
...factor using the rule for a difference of two squares.
($a^{2}-b^{2}=(a+b)(a-b),\ a=k,\ b=8$)
$=(k+8)(k-8)$
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