**Approximate $\:\mathbf{f(x) = 1/\sqrt{x^3 + 1}}\:$ by a polynomial of degree 3 centered at a = 2.**

What exactly is this question asking when it says "approximate"? What is the end result supposed to be I'm so lost 

I found the derivatives(up to the 3rd) and I substituted x with 2, but now what?

I'd appreciate any help!