Evaluating Sum: \sum_{n=0}^N\frac{\cos{n\theta}}{\sin^n{\theta}}

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SUMMARY

The discussion focuses on evaluating the sum \(\sum_{n=0}^N\frac{\cos{n\theta}}{\sin^n{\theta}}\). Participants reference previous evaluations of \(\sum_{n=0}^N\cos{n\theta}\) and \(\sum_{n=0}^N\sin{n\theta}\) using geometric series and De Moivre's Theorem. The challenge lies in applying these methods to the current sum, particularly in leveraging the properties of complex numbers and their real and imaginary components.

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Homework Statement


Evaluate the sum
\sum_{n=0}^N\frac{\cos{n\theta}}{\sin^n{\theta}}

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The Attempt at a Solution


In class we evaluated \sum_{n=0}^N\cos{n\theta} and \sum_{n=0}^N\sin{n\theta}, by expanding them as the real and imaginary parts of a geometric series. However, I can't quite seem to figure out to use that for this question. Could someone give me a bump in the right direction?
 
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Maybe De Moivre's Theorem is useful here? Not sure if that's what you meant by expanding as real and imaginary parts.

[cos(theta) + i*sin(theta)]^n = cos(n*theta) + i*sin(n*theta)
 
For example, we used

\sum_{n=0}^{N}\cos{n\theta} = Re(\sum_{n=0}^{N}z^n)

And then use the analytic formula for the RHS.
 

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