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Putnam 1972 B5

Source: Putnam 1972

February 17, 2022
Putnam3D geometrygeometry

Problem Statement

Let A,B,CA,B,C and DD be non-coplanar points such that ∠ABC=∠ADC\angle ABC=\angle ADC and ∠BAD=∠BCD\angle BAD=\angle BCD. Show that AB=CDAB=CD and AD=BCAD=BC.
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