# Math Help - Inverse functions

1. ## Inverse functions

Hi, I gotta show that f(x)=4x^3/(x^2+1) has an inverse and find f(-1)' (2)

I cant seem to find y, and f(-1)(x). After I find that I guess I derivate and put in the derivate=2, but I need some help to get started off

2. I don't know how to do it... but it seems very complicated

http://www.wolframalpha.com/input/?i=x+%3D+\dfrac{4y^3}{y^2+%2B+1}

Especially is this part:

3. Originally Posted by fredrikhoeg
Hi, I gotta show that f(x)=4x^3/(x^2+1) has an inverse and find f(-1)' (2) I cant seem to find y, and f(-1)(x). After I find that I guess I derivate and put in the derivate=2, but I need some help to get started off
One does not need the exact inverse.

$\dfrac{{df^{ - 1} }}{{dx}}(2) = \dfrac{1}{{f'(f^{ - 1} (2))}}$