Answer
$(-\infty,-4]\cup[4,\infty)$
Work Step by Step
The equation under the square root must be non-negative because the square root function is undefined for negative numbers.
This implies that
$x^2-16\geq0\\x^2\geq16\\|x|\geq4$
Therefore, the required domain is:
$(-\infty,-4]\cup[4,\infty)$
