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parallel lines inside a parallelogram, incircle related

Source: Czech And Slovak Mathematical Olympiad, Round III, Category A 2013 p3

February 13, 2020
geometryparallelogramincircleparallel

Problem Statement

In the parallelolgram ABCDBCD with the center SS, let OO be the center of the circle of the inscribed triangle ABDABD and let TT be the touch point with the diagonal BDBD. Prove that the lines OSOS and CTCT are parallel.