IMO PROBLEM 1963

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MATHPRITOM
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IMO PROBLEM 1963

Unread post by MATHPRITOM » Mon May 02, 2011 7:50 pm

Prove that,cos $\frac{\pi}{7}$-cos$\frac{2\pi}{7}$+cos$\frac{3\pi}{7}$=$\frac{1}{2}$.

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