## An Integral Identity from Physics (Open)

Summary: Prove \frac{\pi^2}{6} = \zeta(2) = \int_0^{\infty} \frac{dx}{x} \int_0^{x} \frac{dy}{y} \{\cos(x-y)-\cos x\}.

Classification: Primary, Classical Analysis; Secondary, Integrals

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**Z. K. Silagadze**

Budker Institute of Nuclear Physics and

Novosibirsk State University

630 090, Novosibirsk, Russia

Email: silagadze@inp.nsk.su