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Puzzle # 121  Italiano italiano Français francais
Difficulty level: bulbbulb, general math knowledge.
Circle vs square
  
The diameter a of the large semicircle below is 10 cm long. Knowing that one of the vertices of the square meets the circumference of the small circle at point P (see diagram below), try to guess the area of the blue square WITHOUT using trigonometry!

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Keywords: sangaku.

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- Perpendicular or not?
- Ratio of similar triangles.

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