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2011 Lusophon Mathematical Olympiad - Problem 5

Source: 2011 Lusophon Mathematical Olympiad - Problem 5

September 17, 2011
geometryrectanglesymmetrygeometric transformationparallelogramreflectionrotation

Problem Statement

Consider two circles, tangent at TT, both inscribed in a rectangle of height 22 and width 44. A point EE moves counterclockwise around the circle on the left, and a point DD moves clockwise around the circle on the right. EE and DD start moving at the same time; EE starts at TT, and DD starts at AA, where AA is the point where the circle on the right intersects the top side of the rectangle. Both points move with the same speed. Find the locus of the midpoints of the segments joining EE and DD.