Answer
$(-\infty,-8) $
Work Step by Step
Step 1. Factor and identify boundary points (zeros) $x^2(x+8)\lt0$ as $x=-8,0$ which divide the x-axis into three intervals $(-\infty,-8),(-8,0),(0,\infty)$
Step 2. Choose test values in each interval $x=-9,-1,1$ and test the inequality to get $True,\ False,\ False$
Step 3. Thus the solution interval is $(-\infty,-8) $