Problem 649: Archimedes' Book of Lemmas: Proposition 10, Tangent,
Chord, Parallel

AB and AC are two tangents to a circle and AD cuts it. Let CE be the chord through C parallel to AD, and let BE meet AD in F. Then, if FG be drawn perpendicular to CE, it will bisect it in G.
See also
iPad Productivity Apps; Adobe Spark Post