Bottema's Theorem.
Invariance of an isosceles right triangle.
Triangle and Squares with Interactive Geometry Software
Step-by-Step construction, Manipulation, and animation.
Kurschak's Tile and Theorem.
Jozsef Kurschak (Hungary, 1864-1933) An elegant and a purely geometric
way of finding the area of a regular dodecagon.
32 congruent isosceles triangles.