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Bisectors and parallels

Source: St Petersburg Olympiad 2013, Grade 9, P3

October 13, 2017
geometry

Problem Statement

ABCABC is triangle. l1l_1- line passes through AA and parallel to BCBC, l2l_2 - line passes through CC and parallel to ABAB. Bisector of ∠B\angle B intersect l1l_1 and l2l_2 at X,YX,Y. XY=ACXY=AC. What value can take ∠A−∠C\angle A- \angle C ?
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