Question Number 28830 by abdo imad last updated on 30/Jan/18
$${let}\:{give}\:{f}\left({x}\right)=\:{ch}\left(\alpha{x}\right)\:{and}\:\mathrm{2}\pi\:{periodic}\:{with}\:\alpha\neq\mathrm{0} \\ $$$${developp}\:{f}\:{at}\:{fourier}\:{series}. \\ $$