I guess this isn't really homework; I had homework problems from this book assigned in my QM classes in college, but this one was never assigned, probably because it's too trivial and I'm just trying too hard. Recently, though, I've decided to go through all of my old physics textbooks and do every last problem in them. I'm not too far along yet. BTW, this problem comes from Griffiths' Intro to QM, 2nd ed. (1.16) Problem states: show that d/dt of the integral from neg. to pos. inf. of Psi(1)*Psi(2) dx = 0 , where Psi(1) and Psi(2) are any (normalizable) solutions to Schrodinger. [Of course, by Psi(1)*, I mean complex conj. of Psi(1), which basically makes this problem "show that the time derivative of the inner product of two normalizable SE solutions is 0."] I think I know of a way to do it using a method not mentioned in the first chapter of Griffiths, but I'm assuming he wouldn't have put it at the end of the first chapter unless you could solve it using those methods. That's what I'm looking for. So far, this seems similar to the example of proving the time derivative of the inner product of a wave function with itself is zero, and so I've been trying to use the same method, but I keep ending up with nasty potentials that I'm not sure I can just blink away. Maybe I'm trying to be a bit too pedantic, or maybe I'm just missing the point altogether. As I'm working through these on my own, I don't expect answers, but a nudge would be helpful.