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whatisreality

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## Homework Statement

I'm not 100% sure what this type of problem is called, we weren't really told, so I'm having trouble looking it up. I'd really appreciate any resources that show solved examples, or how to find some!

Anyway. For the solution to the spherical wave equation φ(t, θ, Φ)

i) Calculate φ( 0, θ, Φ) and ##\frac{\partial φ}{\partial t}##(0, θ, Φ) in terms of A

_{nm}and B

_{nm}.

ii)Let the initial value of φ be given by φ( 0, θ, Φ) = ##Y_{3}^{-2}##

and

##\frac{\partial φ}{\partial t}##(0, θ, Φ) = 16##Y_{2}^{2}##

## Homework Equations

##P_{n}^{m}(z) = \frac{1}{2^n n!}(1-z^2)^{0.5m} \frac{d^(n+m)}{dz^(n+m)}(z^2-1)^n## (1)

##Y_{n}^{m}(\theta, \phi) = (\frac{2n+1}{4 \pi} \frac{(n-m)!}{(n+m)!})^{0.5} e^{im \phi}P_{n}^{m}(cosθ)## (2)

General solution:

φ = ΣΣ ##A_{nm} cos(t \sqrt{n(n+1)}) + B_{nm}sin(t \sqrt{n(n+1)})##

3. The Attempt at a Solution

3. The Attempt at a Solution

I've done part one.

φ( 0, θ, Φ) = ΣΣ ##A_{nm}Y_{n}^{m}(\theta, \phi)## from just subbing in t= 0 to the general solution.

##\frac{\partial \phi}{\partial t}(0,\theta,\phi) =##ΣΣ##B_{nm} \sqrt{n(n+1)}Y_{n}^{m}(\theta, \phi)##

But for part two, I don't know what to do with the initial values! If φ( 0, θ, Φ) = ##Y_{3}^{-2}## then does that mean m = -2 and n = 3 for the whole equation? Presumably not or ##A_{nm}## = 0.

And I can't actually evaluate ##Y_{3}^{-2}##. Because subbing m and n into equation two means I have to also work out P from equation 1. So sub in z = cosθ in this case, but how can I differentiate with respect to cosθ? That doesn't make sense!

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