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Mimimum radius of three semicircles in rectangle

Source: 2023 Israel National Olympiad P5

December 16, 2022
geometrygeometric inequalityrectangle

Problem Statement

Let ABCABC be an equilateral triangle whose sides have length 11. The midpoints of AB,BCAB,BC are M,NM,N respectively. Points K,LK,L were chosen on ACAC so that KLMNKLMN is a rectangle. Inside this rectangle are three semi-circles with the same radius, as in the picture (the endpoints are on the edges of the rectangle, and the arcs are tangent). Find the minimum possible value of the radii of the semi-circles.