Five More Proofs of the Cosine Addition Formula (Inspired by Mark Levi's Perpetuum Mobile Proof)

By Doron Zeilberger

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(Exclusively published in the Personal Journal of Shalosh B. Ekhad and Doron Zeilberger)

Written: April 17, 2022.

Inspired by Mark Levi's wonderful proof of the Cosine addition formula, that showed that it follows from the sad fact that Perpetual Motion is impossible, we recall five other proofs.

Added May 9, 2022: This little gem was narrow-mindedly rejected by the "bouncers" (what is euphemistically called "moderators") of, and upheld by one of the moderators, whom I know personally, Professor Victor Reiner (see rebuttal). While I am very diappointed that Professor Reiner, and the other "three moderators who looked at my appeal" (per Greg Kuperberg) failed to see the value of this little gem, I do thank Professor Reiner for telling me of an alternative, less "selective" repository, called viXra. This little gem is now also posted here.

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