Ab=ac or a=90
Source: Romanian TST 1995,problem1
March 9, 2006
geometryincentercircumcircleconicsellipseperpendicular bisectorgeometry unsolved
Problem Statement
Let AD be the altitude of a triangle ABC and E , F be the incenters of the triangle ABD and ACD , respectively. line EF meets AB and AC at K and L. prove tht AK=AL if and only if AB=AC or A=90