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Proposition: 11.02: Two Intersecting Straight Lines are in One Plane

(Proposition 2 from Book 11 of Euclid's “Elements”)¹

If two straight lines cut one another then they are in one plane, and every triangle (formed using segments of both lines) is in one plane.

• For let the two straight lines $AB$ and $CD$ have cut one another at point $E$.
• I say that $AB$ and $CD$ are in one plane, and that every triangle (formed using segments of both lines) is in one plane.

Modern Formulation

(not yet contributed)

Table of Contents

Proofs: 1

Mentioned in:

Proofs: 1 2 3

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

Github:

non-Github:

@Fitzpatrick

References

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", https://proofwiki.org/wiki/Main_Page, 2016

Footnotes