Anne Fontaine and Susan Hurley, Proof by picture: Products
and reciprocals of diagonals length ratios in the regular polygon, Forum Geometricorum,
6 (2006) 97--101.
Abstract: These ``proofs by picture'' link the geometry of the regular
n-gon to formulae concerning the arithmetic of real cyclotomic fields. We
illustrate the formula for the product of diagonal length ratios and that
for the reciprocal of diagonal length ratio.
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