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## Homework Statement

This is a question regarding Fourier series.

∫ dx |f(x)|^2 = ∑ |Cn|

^{2}(note the integral is between -π and π, and the sum is from n= -∞ to ∞)

## Homework Equations

Complex Fourier series: f(x) = ∑Cn e

^{inx}(again between n = -∞ and ∞)

## The Attempt at a Solution

So I figured the complex conjugate of the Fourier transform would be:

f

^{*}(x)= ∑ C

^{*}n e

^{-inx}

so |f(x)|

^{2}= ∑ |Cn|

^{2}(as the exponentials cancel)

But I don't understand how the integral comes into things? I think I'm just not overly good at manipulating summations etc, so any help would be greatly appreciated!

Thanks.