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ASU 253 All Soviet Union MO 1978 equal angles given and wanted, parallelogram

Source:

July 6, 2019
geometryparallelogramequal angles

Problem Statement

Given a quadrangle ABCDABCD and a point MM inside it such that ABMDABMD is a parallelogram. ∠CBM=∠CDM \angle CBM = \angle CDM. Prove that the ∠ACD=∠BCM \angle ACD = \angle BCM.
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