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imc

geometry intermediate

Problem

A disk of radius rolls all the way around the inside of a square of side length and sweeps out a region of area . A second disk of radius rolls all the way around the outside of the same square and sweeps out a region of area . The value of can be written as , where , and are positive integers and and are relatively prime. What is ?
(A)
(B)
(C)
(D)
Solution
The side length of the inner square traced out by the disk with radius is However, there is a piece at each corner (bounded by two line segments and one arc) where the disk never sweeps out. The combined area of these four pieces is As a result, we have Now, we consider the second disk. The part it sweeps is comprised of four quarter circles with radius and four rectangles with side lengths of and When we add it all together, we have or We equate the expressions for and then solve for We get so the answer is
Final answer
A