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total area of 3 ext. tangent circles with centers on fourth circle <4\pi R^2

Source: 2014 (-15) Swedish Mathematical Competition p2

August 31, 2020
geometryareacirclestangent circles

Problem Statement

Three circles that touch each other externally have all their centers on one fourth circle with radius RR. Show that the total area of the three circle disks is smaller than 4πR24\pi R^2.