Ptolemy Post author By Rik D. Tangerman Post date March 30, 2021 No Comments on Ptolemy Ptolemy’s theorem is a relation between the sides and diagonals of a cyclic quadrilateral: S1*S3+S2*S4=D1*D2. ← Parabola → Midpoint theorem Leave a Reply Cancel replyYour email address will not be published. Required fields are marked *Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ Optionally add an image (JPEG only)