Proposition: Prop. 12.16: Construction of Equilateral Polygon with Even Number of Sides in Outer of Concentric Circles
Euclid's Formulation
There being two circles about the same center, to inscribe an equilateral and evensided polygon in the greater circle, not touching the lesser circle.
 Let $ABCD$ and $EFGH$ be the given two circles, about the same center, $K$.
 So, it is necessary to inscribe an equilateral and evensided polygon in the greater circle $ABCD$, not touching circle $EFGH$.
Modern Formulation
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Table of Contents
Proofs: 1
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Proofs: 1
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References
Adapted from (subject to copyright, with kind permission)
 Fitzpatrick, Richard: Euclid's "Elements of Geometry"
Adapted from CC BYSA 3.0 Sources:
 Prime.mover and others: "Pr∞fWiki", https://proofwiki.org/wiki/Main_Page, 2016