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Previous Puzzles of the Month + Solutions

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Puzzle # 127

Square vs Annulus

In mathematics, an annulus is a ring-shaped geometric figure.
Find a very simple way to calculate the area of the yellow annulus shown below using the following datas:
a) K is the center of the square ABCD,
b) Vertices A and C are on the larger, circonference of the annulus,
c) The area of the square ABCD is 80 cm2.

Difficulty level: , general math knowledge.
Category: Geometry.
Keywords: Pythagorean theorem, annulus, concentric circles, area.
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