Proposition: 1.09: Bisecting an Angle
(Proposition 9 from Book 1 of Euclid's “Elements”)
To cut a given rectilinear angle in half.
 Let $BAC$ be the given rectilinear angle.
 So it is required to cut it in half.
Modern Formulation
It is possible to bisect a given angle \(\angle{BAC}\).
Table of Contents
Proofs: 1
Mentioned in:
Corollaries: 1
Proofs: 2 3 4 5 6
Propositions: 7 8
Sections: 9
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References
Adapted from CC BYSA 3.0 Sources:
 Callahan, Daniel: "Euclid’s 'Elements' Redux" 2014
Adapted from (Public Domain)
 Casey, John: "The First Six Books of the Elements of Euclid"
Adapted from (subject to copyright, with kind permission)
 Fitzpatrick, Richard: Euclid's "Elements of Geometry"