Even for HN, it is easy to prove that HN=HM=2 (the center line of the triangle), HN is perpendicular to BD, and the angle MHD= the angle ABD=30 degrees, so the triangle MHN is an isosceles triangle with the vertex angle of 120 degrees and the waist length of 2. As the height on the cardinal number MN, it is easy to find that MN=2 times the root number 3.