Proposition: 6.21: Similarity of Polygons is Transitive
(Proposition 21 from Book 6 of Euclid's “Elements”)
(Rectilinear figures) similar to the same rectilinear figure are also similar to one another.
* Let each of the rectilinear figures $A$ and $B$ be similar to (the rectilinear figure) $C$.
* I say that $A$ is also similar to $B$.
Modern Formulation
The similarity of rectilinear figures is transitive.
Table of Contents
Proofs: 1
Mentioned in:
Proofs: 1 2 3 4
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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