we have the function
f(x)=x^3(e^x)
using a graphing tool
graph the function
see the attached figure
we have that
The function is decreasing in the interval
[tex](-\infty,\text{ -3)}[/tex]The function is increasing in the interval
[tex](-3,\text{ 0})\text{ U (0,}\infty)[/tex]