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Question Number 92769 by mathmax by abdo last updated on 09/May/20
$${calculate}\:\sum_{{k}=\mathrm{0}} ^{{n}−\mathrm{1}} \:{C}_{{n}} ^{{k}} \:{cos}^{\mathrm{2}} \left(\frac{{k}\pi}{{n}}\right)\:\:\:\:\:\left({n}\geqslant\mathrm{2}\right) \\ $$