Online Geometry Problem 811: Trisecting a Line Segment AB with four
Circles and one Line,
Radius, Center, Diameter, Chord. Level: High School,
SAT Prep, College,
Mathematics Education

The figure below shows a line segment AB.
Circle with center A and radius AB cuts BA extended at C. Circle with
center B and radius BC cuts AB extended at D. Circle with center D and
radius DA cuts circle A at E. Circle with center E and radius EA cuts AB
at F.
Prove that F trisects AB (i.e., AF = AB / 3).