Let ABC be a triangle contained in one of the halfplanes determined by a line r. Points A′,B′,C′ are the reflections of A,B,C in r, respectively. Consider the line through A′ parallel to BC, the line through B′ parallel to AC and the line through C′ parallel to AB. Show that these three lines have a common point. geometryreflectionconcurrencyconcurrentparallel