Let's evaluate the limit of $x^3$ when $x\to \mathrm{-\infty }$

ⓘ A quantity that grows without bound raised to a positive power still grows without bound, to a negative power it tends to 0

So the limit of $x^3$ is $\mathrm{-\infty }$ when $x\to \mathrm{-\infty }$

▶Limit:   $\mathrm{-\infty }$