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Proofs Without Words

A Cosine Product Identity

Pages 329-330 | Received 31 Aug 2022, Accepted 18 Dec 2022, Published online: 12 Apr 2024
 

Summary

We show visually that cos(π/7)cos(2π/7)cos(3π/7)=1/8 and discuss a generalization.

Acknowledgment

The author wishes to thank an anonymous reviewer and the Editor for helpful suggestions on an earlier draft of this note.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Roger B. Nelsen

ROGER NELSEN (MR Author ID: 237909) is a professor emeritus at Lewis & Clark College, where he taught mathematics and statistics for 40 years.

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