MathDB

4

Part of 2019 Chile National Olympiad

Problems(1)

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

Source:

2/17/2021
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.
geometryparallelequal angles