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## Homework Statement

Hi all.

Please take a look at the lowest equation in this picture:

http://img143.imageshack.us/img143/744/picture2ao8.png [Broken]

This is Parselvals Identity.

Let us say that I am given a Fourier series of f(x), and I want to calculate the integral of f(x)^2 from -L to L. In order to do this, I use Parsevals Identity. But the

**requirement**for me to use Parsevals Identity is that the series is well-defined and square integrable. How do I show this?

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