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## 'The Pillar of Chios' printed from http://nrich.maths.org/

Semicircles are drawn on the sides of a rectangle ABCD as shown
in the diagram. A circle passing through points ABCD carves out
four crescent-shaped regions (coloured yellow and green in the
diagram).

Prove that the sum of the areas of the four crescents is equal
in area to the rectangle ABCD.