29 Oct
2011
29 Oct
'11
8:33 p.m.
On Sat, Oct 29, 2011 at 5:27 PM, Fred lunnon <fred.lunnon@gmail.com> wrote:
Richard's paper mentions mentions that the 4 altitude lines of a tetrahedron, through vertices and perpendicular to faces, do not necessarily concur in a common point.
I seem to recall that if one pair of altitudes is intersecting, then the other pair is as well. Does anyone know an easy proof or counterexample? --Joshua Zucker