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Prove that angle ABC > 120°

Source: Tuymaada 2009, Junior League, First Day, Problem 3

July 19, 2009
trigonometrygeometry unsolvedgeometry

Problem Statement

In a cyclic quadrilateral ABCD ABCD the sides AB AB and AD AD are equal, CD>AB\plus{}BC. Prove that ∠ABC>120∘ \angle ABC>120^\circ.
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