We got given this problem in a tutorial a few weeks ago and I can't for the life of me figure out how to solve it, probably something simple but would love it if someone could tell me how to go about this.

Prove that:

$\displaystyle \frac{[x^2(3-x)(2+x)]^\frac{1}{3}}{3+x} \leq 1$ if $\displaystyle |x| \leq 1$

Cheers