Euclidean and curved-surface geometry
Triangle-angle relations depend on the geometry.
Key knowledge
Nondegenerate Euclidean triangles have angle sum π. Geodesic triangles in the hyperbolic plane have smaller angle sum; ordinary spherical geodesic triangles have larger angle sum.
Conditions and scope
- On a sphere use simple triangles with shorter great-circle arcs contained in an open hemisphere.
- Angles are intrinsic; Euclidean Pythagoras cannot be transferred unchanged to curved surfaces.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Triangle-angle comparison of Euclidean, spherical and hyperbolic geometries; historical/priority commentary excluded.
2026-10-10 · Bounded triangle-angle comparison, not a full classification of geometries.
Entry details
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- math-non-euclidean-geometry
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