Chapter IV: The Quadrilateral

Varignon Parallelogram, Bimedians, Ptolemy’s Theorem, Anticenter, Brahmagupta, Circumscriptible & Bicentric Quadrilaterals

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• Archival Span: Folios 0143–0158 · Printed Pages 124–139 · Articles §§ 240–281

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• Companion Track: Switch to the Commentary tab above for mathematical synthesis, triangle-center mappings, and GEOMETOR connections.

Section & Article Conspectus

Section	Title	Folios	Pages	Articles
A	The General Quadrilateral	0143–0146	124–127	§§ 240–250
B	The Cyclic Quadrilateral (incl. Ptolemy’s Theorem § 255 & Anticenter)	0146–0154	127–135	§§ 251–267
C	Other Quadrilaterals (Circumscriptible & Bicentric)	0154–0158	135–139	§§ 268–281

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