Math Help - derivative of the inverse

1. derivative of the inverse

Would I be able to take the inverse of 2 first and then enter into f '(x) or do I have to replace f(x) with y(y=sqrt...) and then x with y(x=sqrt..) and solve for y? I'm sorry if its confusing.
Here is the problem:
Let f(x)=sqrt(x^3+x+2), find(f^-1)'(2).

2. Use the Theorem on the derivative of an inverse:

If f(a) = c

Then [f^(-1)] ' (c) = 1 / f '(a)

f(x)=sqrt(x^3+x+2)

f(1) = 2

[f^(-1)] ' (2) = 1 / f '(1)