fourier cosine series

• Oct 14th 2011, 05:27 AM
kittycat485
fourier cosine series
Hi, this question is being a pain to me can someone please help.

a) Find the Fourier cosine series of $f(x)=|sinx|$ for interval $(-\pi, \pi)$.

b) Use it to find the sum

$\sum_{n \ge 1} \frac{1}{4n^2-1}$

Thanks
• Oct 14th 2011, 06:16 AM
DeMath
Re: fourier cosine series
• Oct 15th 2011, 05:01 AM
kittycat485
Re: fourier cosine series
wow, thanks demath, I was just thrown a bit by the absolute sign. I understand it now.