Question Number 64498 by slotto last updated on 18/Jul/19
$$\mathrm{please},\:\mathrm{anyone}\:\mathrm{help}\:\mathrm{me}\:\mathrm{to}\:\mathrm{solve}\:\mathrm{this} \\ $$$$\mathrm{i}.\:\underset{\mathrm{k}=\mathrm{1}} {\overset{\mathrm{n}} {\sum}}\mathrm{cos}\left(\frac{\mathrm{k}^{\mathrm{2}} \pi}{\mathrm{n}}\right) \\ $$$$\mathrm{ii}.\:\underset{\mathrm{k}=\mathrm{1}} {\overset{\mathrm{n}} {\Sigma}}\mathrm{sin}\left(\frac{\mathrm{k}^{\mathrm{2}} \pi}{\mathrm{n}}\right) \\ $$$$\mathrm{thank}\:\mathrm{you}. \\ $$