Question Number 126503 by benjo_mathlover last updated on 21/Dec/20
$$\:{solve}\:{f}\:'\left({x}\right)={f}\left({x}+\frac{\pi}{\mathrm{2}}\right)\: \\ $$
Commented by Dwaipayan Shikari last updated on 21/Dec/20
$${f}\left({x}\right)={cosx} \\ $$