The expression $Ce^{-x} + Ce^{-x}$ can be simplified by combining like terms.

$Ce^{-x} + Ce^{-x} = 2Ce^{-x}$

Thus, the simplified expression is:

$2Ce^{-x}$

Would you like more details on this simplification or any related topics? Here are some follow-up questions you might find helpful:

1. What are the properties of exponential functions like $e^{-x}$?
2. How does the constant $C$ affect the behavior of this function?
3. Can we differentiate or integrate the function $2Ce^{-x}$?
4. How would this expression change if there were different exponents?
5. How can exponential decay be applied in real-world problems?

Tip: When simplifying expressions, always look for like terms that can be combined, especially when dealing with constants and similar exponential factors.