#### Answer

$(x-4+y)(x-4-y)$

#### Work Step by Step

Since the first 3 terms of the given expression, $
x^2-8x+16-y^2
$, form a perfect square trinomial, then,
\begin{array}{l}
(x^2-8x+16)-y^2
\\\\=
(x-4)^2-y^2
.\end{array}
Using $a^2-b^2=(a+b)(a-b)$ or the factoring of the difference of two squares, then,
\begin{array}{l}
(x-4)^2-y^2
\\\\=
[(x-4)+y][(x-4)-y]
\\\\=
(x-4+y)(x-4-y)
.\end{array}