# Sine series for cos(x) (FOURIER SERIES)

 HW Helper Thanks PF Gold P: 7,642 If you have expanded cos(x) in a sine series using $p = 2\pi$ in the formula $$b_n = \frac 2 p \int_0^p \cos(x) \sin{\frac{n\pi x}{p}}\,dx$$ what you are representing is the $4\pi$ periodic odd extension of cos(x). [edit - corrected typo: bn not an]