Fourier series of the periodic function (period 2π) defined by f(x) = {0, −π <…

Fourier series of the periodic function (period 2π) defined by f(x) = {0, −π < x < 0; x, 0 < x < π} is π/4 + Σₙ₌₁∞[(1/(πn²))(cos nπ − 1) cos nx − (1/n) cos nπ sin nx]. But putting x = π, we get the sum of the series 1 + 1/3² + 1/5² + 1/7² + … is