Answer
$(-\infty,-2]U[2,\infty)$
Work Step by Step
Step 1. Graph $f(x)=-2(x+2)(x-2)^3$ as shown in the figure.
Step 2. The x-intercepts form three intervals $(-\infty,-2],[-2,2],[2,\infty)$
Step 3. For $f(x)\le0$, we can identify the solution intervals as $(-\infty,-2]U[2,\infty)$
