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Archimedes' Book of Lemmas: Proposition 8  Angle trisection 
If CD be any chord of a circle whose
center is O, and if CD be produced to A so that AD is equal to
the radius; if further AO meets the circle in B, then the angle
BOC will be equal to three times the angle BAC.
This is the Archimedes' neusis
construction to the angle trisection problem. "Neusis" means
use of a marked ruler
in Greek. 

