Originally Posted by

**galactus** Hello all:

I seen a problem on another site where someone was wanting to know the inverse.

$\displaystyle y=4+x+5e^{x-3}$

As Plato said, the derivative is always positive, so it has an inverse, but can not be found by elementary means.

I ran it through Maple and it kicked back:

$\displaystyle x=y-4-LambertW(\frac{5e^{y}}{e^{7}})$

What is Lambert?. I am unfamiliar. Does anyone know how this would be done without technology?. I thought it would something interesting to look into. I did find an interesting page on Wiki