Proposition: Prop. 9.11: Elements of Geometric Progression from One which Divide Later Elements
(Proposition 11 from Book 9 of Euclid's “Elements”)
If any multitude whatsoever of numbers is in continued proportion, (starting) from a unit, then a lesser (number) measures a greater according to some existing (number) among the proportional numbers.
 Let any multitude whatsoever of numbers, $B$, $C$, $D$, $E$, be in continued proportion, (starting) from the unit $A$.
 I say that, for $B$, $C$, $D$, $E$, the least (number), $B$, measures $E$ according to some (one) of $C$, $D$.
Modern Formulation
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Table of Contents
Proofs: 1 Corollaries: 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