I'm having trouble finding the absolute max and min. This is the question:

Find the absolute maximum and absolute minimum values of f(x)=(x^(2/3))*((x^2)-4)

This is what I have so far:

F'(x)=(8/(3(x^1/3)))*((x^2)-1)

Critical #'s I got: x=0(undefined), x=1, x=-1.

Now I don't know if I got the right critical #'s and also I dont know if I have to plug them back into the f(x) or f'(x).

Any help?