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2. Relevant equations

3. The attempt at a solution

i'm pretty much learning fourier series from scratch today after only looking at it in lectures (and my exam is tomorrow lol @ me) and i'm sort of stuck.

The solutions have something different to what i have, i think it might be an error in their integration by parts (which i also learnt today, despite how simple it seems).

this is my working out: http://i.imgur.com/6OXlr.jpg

and this is the worked solutions: http://i.imgur.com/1RAJL.png

doesnt the integral of (1/n)*sin(nx) equal to (-1/n^2)*cos(nx)? like i have in my working?

because the solutions are saying it integrates into (-1/n)*cos(nx).

or is mine set out incorrectly after i've integrated by parts?

edit: i've only shown both workings from where i had to find a subscript n, before that everything was fine and correct.

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# Fourier series question, either i'm wrong or the answers are wrong

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