/sci/ - Science & Math

Hi guys.
I've been having problems with a calculus example exercise. In the image, as you can see, the exercise is solved in three steps after the "Original" exercise: "Rewriting", "Integrate" and "Simplifying".
The thing is I have no idea what did they do to the "Original" to obtain the "Rewriting" step:
they turned this "cbrt(x)(x - 4)" where cbrt is cubic root,
into this "x^(4/3) - 4 x^(1/3)".
If the exercise where to begin in the "Rewriting" step i would't have any problems whatsoever.
So i'm not asking you to help me solve the entire exercise, I only want you explain me what happened between "Original" and "Rewriting".
I don't care if you call me stupid for this, but i would really appreciate it if you can help me with this one.
Forgive me if i sound rude or just stupid. English is not my main language.
Thanks beforehand guys.