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EF//CD wanted, <ADC = <BCD > 90^o, // (Chile 2019 L2 P4)

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February 17, 2021
geometryparallelequal angles

Problem Statement

In the convex quadrilateral ABCDABCD , ∠ADC=∠BCD>90o\angle ADC = \angle BCD > 90^o . Let EE be the intersection of the line ACAC with the line parallel to ADAD that passes through BB. Let FF be the intersection of line BDBD with the line parallel to BCBC passing through AA. Prove that EFEF is parallel to CDCD.
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