Proposition: 1.23: Constructing an Angle Equal to an Arbitrary Rectilinear Angle

(Proposition 23 from Book 1 of Euclid's “Elements”)

To construct a rectilinear angle equal to a given rectilinear angle at a (given) point on a given straight line.


Modern Formulation

It is possible to construct an angle $\angle{FAG}$ equal to an arbitrary angle $\angle{CDE}$ on an endpoint of a given segment $\overline{AB}.$

Proofs: 1

Proofs: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Sections: 19

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



Adapted from CC BY-SA 3.0 Sources:

  1. Callahan, Daniel: "Euclid’s 'Elements' Redux" 2014

Adapted from (Public Domain)

  1. Casey, John: "The First Six Books of the Elements of Euclid"

Adapted from (subject to copyright, with kind permission)

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