Answer
$(-\infty,-2]\cup[2,\infty)$.
Work Step by Step
Step 1. With the domain requirements, we have $x^4-16\ge 0 \Longrightarrow (x^2+4)(x+2)(x-2)\ge0$, identify boundary points as $x=-2,2$.
Step 2. Form intervals $(-\infty,-2],[-2,2],[2,\infty)$.
Step 3. Choose test values for each 1interval $x=-3,0,3$.
Step 4. Test the inequality to get results: $True,\ False,\ True $
Step 5. We have the solution $(-\infty,-2]\cup[2,\infty)$.
