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. fig01e

Modern Formulation

Proofs: 1

Proofs: 1

Thank you to the contributors under CC BY-SA 4.0!



Adapted from (subject to copyright, with kind permission)

  1. Fitzpatrick, Richard: Euclid's "Elements of Geometry"

Adapted from CC BY-SA 3.0 Sources:

  1. Prime.mover and others: "Pr∞fWiki",, 2016