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**Honore**- Replies: 4

Hello,

Since I could not solve the following equation though applying all information I have about trigonometry, I would very appreciate if anybody could help or make some suggestion. Thanks for your time.

cos(2pi/11)+cos(4pi/11)+cos(6pi/11)+cos(8pi/11)+cos(10pi/11)=?

(Answer: -1/2)

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