Morrie's Law
| cos(20 degrees)cos(40 degrees)cos(80 degrees)=1/8. |
An identity communicated to Feynman as a child by a boy named Morrie Jacobs (Gleick 1992, p. 47). Feynman remembered this fact all his life and referred to it in a letter to Jacobs in 1987 (Gleick 1992, p. 450). It is a special case of the general identity
with k=3 and a=20 degrees (Beyer et al. 1996).
See also
Trigonometry Angles, Trigonometry Angles--Pi/9Explore with Wolfram|Alpha
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References
Anderson, E. C. "Morrie's Law and Experimental Mathematics." J. Recr. Math. 29, 85-88, 1998.Beyer, W. A.; Louck, J. D.; Zeilberger, D. "A Generalization of a Curiosity that Feynman Remembered All His Life." Math. Mag. 69, 43-44, 1996.Gleick, J. Genius: The Life and Science of Richard Feynman. New York: Pantheon Books, pp. 47 and 450, 1992.Referenced on Wolfram|Alpha
Morrie's LawCite this as:
Weisstein, Eric W. "Morrie's Law." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/MorriesLaw.html