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Fall 2021 AMC 10 B

United States 2021 geometry

Problem

A regular hexagon of side length is inscribed in a circle. Each minor arc of the circle determined by a side of the hexagon is reflected over that side. What is the area of the region bounded by these reflected arcs? (A) (B) (C) (D) (E)
Solution
Note that the reflected arcs do not overlap except at their endpoints. The area of the region can be found by subtracting from the area of the hexagon the difference between the areas of the circle and the hexagon. This is equivalent to twice the area of the hexagon minus the area of the circle. Therefore the requested area is
Final answer
B

Techniques

CirclesTrianglesConstructions and loci