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The area of a regular Dodecagon - Kürschák's Tile

This applet demonstrates an elegant method for finding the area of a regular dodecagon. The construction is based on the tiling of the dodecagon consisting of 12 equilateral triangles and 24 isosceles triangles. This tiling is known as Kürschák’s tile. Given is a circle with radius , the inscribed regular dodecagon, and the circumscribed square.
  • Click the “Tile Dodecagon” button.
  • Click the "Rearrange" button.
  • Find the area of the dodecagon as a fraction of the area of the square.
What additional proofs are needed to justify the construction?