Answer
$\color{}(x+y-4)(x-y-4)$
Work Step by Step
Group the first three terms together to obtain:
$=(x^2-8x+16)-y^2$
The trinomial is a perfect square trinomial in the form $a^2-2ab+b^2$ with $a=x$ and $b=4$.
RECALL:
$a^2-2ab+b^2=(a-b)^2$
Use the formula above to obtain:
$=(x-4)^2-y^2$
The polynomial above is a difference of two squares.
Factor using the formula $a^2-b^2=(a-b)(a+b)$ with $a=x-4$ and $b=y$ to obtain:
$=[(x-4)+y][(x-4)-y]
\\=(x-4+y)(x-4-y)
\\=\color{}(x+y-4)(x-y-4)$
