1. ## Inverse function

If f(x) = ln 4x, what is the value of f^-1(6). (The f raises to the -1 is the inverse function of f(x).

2. ## Re: Inverse function

So, let y = ln(4x). How, in general, do you invert functions?

3. ## Re: Inverse function

The natural log (ln) has a base e, so another way of rewriting f(x) = ln 4x or y = ln 4x:
$e^{y} = 4x$
$\frac{e^{y}}{4} = x$

y = 6. Substituting it into this equation and solving for x will yield approximately 100.86.