# Homework Help: Derivative of a complex conjugate?

1. Sep 20, 2010

### xago

1. The problem statement, all variables and given/known data

[PLAIN]http://img823.imageshack.us/img823/4500/85131172.png [Broken]

2. Relevant equations

Derivations and substitutions.

3. The attempt at a solution

Basically it seems like a very simple problem to me however I can't seem to get the right answer. First I just assumed that the c.c. (complex conjugate) was just a constant thus:

$$\Psi$$'(x) = Ckeikx
$$\Psi$$''(x) = Ck2eikx

But substituting that equation into the original DE gives:

Ck2eikx = Ck2eikx + k2(c.c)

obviously I'm missing something.

edit: maybe I read the question wrong could c.c. mean Ce-ikx ???

Last edited by a moderator: May 4, 2017
2. Sep 20, 2010

### Dick

Yes, the complex conjugate of exp(ikx) is exp(-ikx). And don't forget the c.c. of C is C^*. And d/dx(exp(ikx)) isn't k*exp(ikx) either, it's ik*exp(ikx).

3. Sep 20, 2010

### xago

Ok, I understand now. Also thanks for pointing out my derivative mistake!