# fourier cosine series

• October 14th 2011, 04:27 AM
kittycat485
fourier cosine series

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
• October 14th 2011, 05:16 AM
DeMath
Re: fourier cosine series
• October 15th 2011, 04:01 AM
kittycat485
Re: fourier cosine series
wow, thanks demath, I was just thrown a bit by the absolute sign. I understand it now.