[SOLVED] Sum of exponentials

Hi folks,

This is not for "homework" per se, it's actually for work - I'm trying to model something. I won't bore you with the details, but the basics of the problem boil down to being able to reduce the expression:

e^(ax) + e^(bx)

To a single term. I assumed that I may be able to express it as

e^(cx)

and tried to find the value of c that satisfied the first expression. However, this required that the value of c varied with x, so it seems that assumption was wrong.

Anyone know how to solve this problem?