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2022 Polish Junior Math Olympiad First Round P5

Source:

May 21, 2023
geometry

Problem Statement

Points KK, LL, MM lie on the sides BCBC, CACA, ABAB of equilateral triangle ABCABC respectively, and satisfy the conditions KM=LMKM=LM, KML=90\angle KML=90^\circ, and AM=BKAM=BK. Prove that CKL=90\angle CKL=90^\circ.