- #1

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everywhere I can see this

[tex]a_n = \frac{1}{\pi}\int_{-\pi}^\pi f(t) \cos(nt)\, dt[/tex]

[tex]b_n = \frac{1}{\pi}\int_{-\pi}^\pi f(t) \sin(nt)\, dt[/tex]

etc... I can't find, how to derive this formulas. I'm really tired and a bit confused of this formulas, because I can't find possible way to derive them. I don't like only formula application, but I want to know, what is that formula about.

Thank you...