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My QP homework involves (not is) Fourier expansion. i think i'm done with the physics part and for the answer, i need to expand a function to fourier series and solve it. So far well, but I couldn't solve that simple function:

f(x) = x (in -1,1 interval)

I've found various series, but when I graph them, it doesn't match the original function.

I've tried:

[tex]a_0 = \frac{1}{T} \int_0^T {f(x) dx}[/tex]

with T = 4 (well, is it 2 or 4!?), and got 8. similarly

[tex]a_n = \frac{1}{T} \int_0^T{f(x)cos(\frac{2 \pi n}{T}) dx}[/tex]

and evertime I tried to solve, I've just messed it up.

Can someone help?...

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# Fourier series of a lineer function

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