(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A generic state represented by the wave function ##\psi (\vec(x)## can be expanded in the eigenstates with defined angular momentum. Write such an expansion for a plane wave travelling along the z direction with momentum ##p = \hbar k## in terms of unknown coefficients ##c ( k ′ )_ {l m}## . Show that ##c ( k )_{ l m} are non-zero only if k' = k and m = 0

2. Relevant equations

3. The attempt at a solution

I don't know where to start. I could of course go the long way, introducing dimensionless variables, do a power series ansatz and solve de DE with frobinious trick. But it seems the answer will be way easier than that if you just know how to approach it.

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# Homework Help: Expansion of the wave equation for a stationary wave

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