Question Number 34013 by math khazana by abdo last updated on 29/Apr/18
$${find}\:\:\sum_{{n}=\mathrm{0}} ^{\infty} \:\:\:\:\frac{{cos}\left(\left(\mathrm{2}{n}+\mathrm{1}\right)\frac{\pi}{\mathrm{4}}\right)}{\left(\mathrm{2}{n}+\mathrm{1}\right)^{\mathrm{2}} }\:. \\ $$