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Curved Square

Age 16 to 18
Challenge Level Yellow star
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A square of side length 1 has an arc of radius 1 drawn from each of its corners, as in the following diagram. The arcs intersect inside the square at four points, to create the shaded region.

A square, with purple arcs drawn from each corner to the opposite corner, intersecting to make a square-shape with curved sides in the middle


What is the area of the largest square that can be completely contained within the shaded region?

Is this a good estimate of the actual shaded area?

What is the exact area of the central shaded region?
How did that compare to your estimate?

Can you find more than one method to work out the exact area?




Click here for a poster of this problem.

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The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.

NRICH is part of the family of activities in the Millennium Mathematics Project.

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