what do you mean, for x = -1?

I meant something like that. What Function is this?

oh, you might be thinking about logarithmic functions

the natural logarithmic function ln(x) (blue) is the inverse of the exponential function e^x (black)

This is too complicated for me. I'm just a Hauptschulabbrecher.

You don't need to know it to be happy, but I just spent about an hour being fascinated about eulers number, so I drew the picture.