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<MAB=<MCB iff <MBA=<MDA, ABCD # Puerto Rico Ibero IMO TST 2009.4

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September 16, 2021
geometryequal anglesparallelogram

Problem Statement

The point M M is chosen inside parallelogram ABCD ABCD. Show that ∠MAB \angle MAB is congruent to ∠MCB \angle MCB, if and only if ∠MBA \angle MBA and ∠MDA \angle MDA are congruent.
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