Question Number 38107 by maxmathsup by imad last updated on 21/Jun/18
$${find}\:{C}\:=\:\sum_{{n}=\mathrm{1}} ^{\infty} \:\:\:\frac{{cos}\left({nx}\right)}{{n}^{\mathrm{2}} }{dx}\:\:{and}\:{S}=\sum_{{n}=\mathrm{1}} ^{\infty} \:\:\frac{{sin}\left({nx}\right)}{{n}^{\mathrm{2}} } \\ $$