Find the inverse of this function

1. Apr 22, 2014

utkarshakash

1. The problem statement, all variables and given/known data
Let f be a function defined as f:(0,exp-3/2) → [-1/4, ∞),
$f(x) = (ln x)^2 + 3 ln x + 2$ then inverse of f is equal to

3. The attempt at a solution

The two possibilities are
$exp (\dfrac{-3\pm\sqrt{4x+1}}{2})$

How to decide which one is correct?

2. Apr 22, 2014

Pranav-Arora

Try plugging $x=2$ in the inverse function. That should help you in figuring out the correct sign.

3. Apr 22, 2014

LCKurtz

Or note that one of your choices is always negative.