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2002 AMC 10A Problem 19

Problem 19 of 25HarderGeometry

Spot’s doghouse has a regular hexagonal base that measures one yard on each side. He is tethered to a vertex with a two-yard rope. What is the area, in square yards, of the region outside the doghouse that Spot can reach?

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Solution

At the tether vertex the hexagon blocks its 120120^\circ interior angle, leaving a 240240^\circ sector of radius 2:2: area 240360π(2)2=8π3.\dfrac{240}{360}\pi(2)^2=\dfrac{8\pi}{3}. Wrapping around each of the two adjacent vertices, 11 yard of rope remains and sweeps a 6060^\circ sector: 260360π(1)2=π3.2\cdot\dfrac{60}{360}\pi(1)^2=\dfrac{\pi}{3}. The total is 8π3+π3=3π.\dfrac{8\pi}{3}+\dfrac{\pi}{3}=3\pi. Thus, the correct answer is E.

More practice

Concepts: sector · regular polygon · circle area

Problem text and solution from the LIVE past-contest archive. See also the AoPS wiki page for community solutions.