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|BE - CE| < AD \sqrt3 when AB = BC= CD and AD \perp BC

Source: Czech-Polish-Slovak Junior Match 2015, Team p3 CPSJ

March 19, 2020
geometrygeometric inequalityequal segmentsperpendicular

Problem Statement

Different points AA and DD are on the same side of the line BCBC, with AB=BC=CD|AB| = | BC|= |CD| and lines ADAD and BCBC are perpendicular. Let EE be the intersection point of lines ADAD and BCBC. Prove that BECE<AD3||BE| - |CE|| < |AD| \sqrt3