## Detailed description

Triangle ABC with AD the altitude perpendicular to BC, BE the altitude perpendicular to AC and l AD meets BE at H. CH meet AB at F. DE is joined. Let α = ∠BCF, ∠D E H = α and ∠DAB =α.

Triangle ABC with AD the altitude perpendicular to BC, BE the altitude perpendicular to AC and l AD meets BE at H. CH meet AB at F. DE is joined. Let α = ∠BCF, ∠D E H = α and ∠DAB =α.