Proposition: Prop. 9.01: Product of Similar Plane Numbers is Square
(Proposition 1 from Book 9 of Euclid's “Elements”)
If two similar plane numbers make some (number by) multiplying one another then the created (number) will be square.
* Let $A$ and $B$ be two similar plane numbers, and let $A$ make $C$ (by) multiplying $B$.
* I say that $C$ is square.
Modern Formulation
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