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2 common tangents of externally tangent circles are sides of an isosceles

Source: Lusophon 2015 CPLP P5

August 29, 2018
geometrytangent circlesisosceles

Problem Statement

Two circles of radius RR and rr, with R>rR>r, are tangent to each other externally. The sides adjacent to the base of an isosceles triangle are common tangents to these circles. The base of the triangle is tangent to the circle of the greater radius. Determine the length of the base of the triangle.