The common nine-point circle is tangent to all 16 incircles and excircles of the four triangles whose vertices form the orthocentric system.Weisstein, Eric W. "Orthocentric System." From MathWorld--A Wolfram Web Resource.
The common nine-point circle is tangent to all 16 incircles and excircles of the four triangles whose vertices form the orthocentric system.Weisstein ,Eric W. "Orthocentric System." From MathWorld--A Wolfram Web Resource.