MathDB
parallelism and concurrency

Source: ITAMO 2013 problem 5

May 11, 2013
geometrycircumcircleparallelogramrhombusperpendicular bisectorgeometry unsolved

Problem Statement

ABCABC is an isosceles triangle with AB=ACAB=AC and the angle in AA is less than 6060^{\circ}. Let DD be a point on ACAC such that DBC=BAC\angle{DBC}=\angle{BAC}. EE is the intersection between the perpendicular bisector of BDBD and the line parallel to BCBC passing through AA. FF is a point on the line ACAC such that FA=2ACFA=2AC (AA is between FF and CC). Show that EBEB and ACAC are parallel and that the perpendicular from FF to ABAB, the perpendicular from EE to ACAC and BDBD are concurrent.