CK-12 Basic Geometry, Volume 1 of 2 CK-12's Basic Geometry FlexBook, Volumes 1 through 2, is designed to present students with geometric principles in a more graphics-oriented course. Volume 1 includes 6 chapters: Basics of Geometry, Reasoning and Proof, Parallel and Perpendicular Lines, Triangles and Congruence, Relationships with Triangles, and Polygons and Quadrilaterals.