Geometry Problem 640. Archimedes' Book of Lemmas: Proposition 1.
1. Internally Tangent Circles at A
If two circles touch at A (internally), and if BC and DE are parallel diameters, then ACE is a straight line.
2. Externally Tangent Circles at A.
If two circles touch at A (externally), and if BC and DE are parallel diameters, then ACE is a straight line.
Books of Lemmas Index