Answer
$(x+8)(x-16)$
Work Step by Step
$x2-8x-128$ has no common monomial factor
=$(\ \ \ \ \ \ \ \ \ )(\ \ \ \ \ \ \ \ \ )$
=$(x\ \ \ \ \ \ \ )(x\ \ \ \ \ \ \ )$
=$(x+\ \ )(x-\ \ )$ The factors of -128 must have unlike signs.
=$(x+8)(x-16)$ 8 and -16 have a sum of -8 and a product of -128.
