Restrictions on Parameters for Oscillatory Solution in Restricted Domain

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SUMMARY

The discussion centers on the restrictions for parameters A, B, and k in the oscillatory solution defined by the equation \(\psi(x) = A \cos(kx) + B \sin(kx)\) within the domain \(0 \leq x \leq a\). The boundary conditions \(\psi(0) = 0\) and \(\psi(a) = 0\) lead to the conclusion that A must equal zero, resulting in \(B \sin(ka) = 0\). This implies that B must also be zero unless \(k\) is an integer multiple of \(\pi/a\), specifically \(k = n\pi/a\), where \(n\) is a positive integer.

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Homework Statement


For the oscillatory solution (+k2) solution, suppose x is restricted to 0\leqx\leqa by requiring \psi(x)=0 and \psi(a)=0, what are the restrictions on A,B and k?


Homework Equations


given \psi(x)=Acos(kx)+Bsin(kx)


The Attempt at a Solution


so, I pretty just plugged in the zero values to get A must be zero, leaving only \psi(a)=0=Bsin(kx), which implies that B=0 and thus k can be 0 or pi, which seems to be a completely unreasonable result, so I am confused as to where I went wrong? Thanks
 
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You have 0 = sin(ka) not sin(kx). So ka can be any integer multiple of pi: k = nπ/a.
 

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