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Question Number 64498 by slotto last updated on 18/Jul/19

please, anyone help me to solve this

i . \underset{k = 1}{\sum^{n}} \cos (\frac{k^{2} π}{n})

ii . \underset{k = 1}{\overset{n}{Σ}} \sin (\frac{k^{2} π}{n})

thank you .