Question Number 28879 by abdo imad last updated on 31/Jan/18
$${find}\:{the}\:{value}\:{of}\:\sum_{{n}=\mathrm{1}} ^{+\infty} \:\:\frac{{cos}\left({n}\pi{x}\right)}{{n}^{\mathrm{2}} }\:{with}\:\:\mathrm{0}<{x}<\mathrm{1}. \\ $$
find-the-value-of-n-1-cos-npix-n-2-with-0-lt-x-lt-1-