Question Number 35581 by abdo mathsup 649 cc last updated on 20/May/18
$${let}\:{f}\left({x}\right)\:=\:\:\frac{\mathrm{3}}{\mathrm{1}+\mathrm{2}{cosx}}\:\:,\:\mathrm{2}\pi\:{periodic}\:{even} \\ $$$${developp}\:{f}\:\:{at}\:{fourier}\:{serie}. \\ $$$$ \\ $$