Can anyone help me with this?(adsbygoogle = window.adsbygoogle || []).push({});

Show that

[tex]\sum_{n=1}^{\infty}(-1)^{n+1}\frac{\cos{nx}}{n^2} = \frac{\pi^2-3x^2}{12} \quad , \quad x \in [-\pi,\pi].[/tex]

I have tried writing the right-side expression as a Fourier series, but it leads nowhere. What should I do?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Fourier series problem (again)

**Physics Forums | Science Articles, Homework Help, Discussion**