I hope that this is the appropriate forum to ask something about Fourier series.(adsbygoogle = window.adsbygoogle || []).push({});

My question is a little intuitive.Say I expand a function in Fourier series with

n=-∞ to n=∞.The graph of the function is available.

Now suppose,I cut off some terms for which |n|>N and expand the function.It will not be a Fourier series any more.But I am not worried about that.All I want to knowwhether this process is capable to preserve the essential feature of the graph.If terms like that (|n|>N) contribute very small to the actual series,then what I am telling is possible with a good approximation.Please let me know...

I encountered this problem in deriving the Parsevals formula in a Quantum Mechanics book where they have folowed the procedure in"approximation in the mean".

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# Fourier Series confusion

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