Question

does anyone have a link to a good explanation of the rigorous proof of the following:

Answer 1

\[\frac{1}{1^2} + \frac{1}{2^2} + \frac{1}{3^2} + ... + \frac{1}{n^2} + ... = \frac{\pi^2}{6}\]

Answer 2

http://en.wikipedia.org/wiki/Basel_problem#A_rigorous_proof_using_Fourier_series