The Hyperbolic (3,7) Tessellation
Pictured are 7 tiles of the Hyperbolic (3,7) tessellation. Each triangular tile is regular, congruent with all the others, and tessellates with 7 copies of itself at each vertex. Adjust A and B to explore. As you do so, the triangles always remain congruent (in the Hyperbolic sense).
What must the angle be at each vertex of the above regular triangles?