Euclidean, affine, hyperbolic, and spherical geometries
Build geometry from first principles using axiomatic systems
Explore classical Euclidean results with rigorous proofs
Study geometry without distance - parallelism and ratios
Extend the plane with points at infinity and projective transformations
Explore the geometry where parallel lines diverge
Geometry on the surface of a sphere - where lines always meet
The geometry of positive curvature and the projective plane
Compare Euclidean, hyperbolic, and elliptic geometries
Comprehensive resources for proof-based geometry