Hans Havlicek, Gunter Weiß. Altitudes of a Tetrahedron and Traceless Quadratic Forms. The American Mathematical Monthly, 110(8):679-693, 2003. [doi]
@article{HavlicekW03,
title = {Altitudes of a Tetrahedron and Traceless Quadratic Forms},
author = {Hans Havlicek and Gunter Weiß},
year = {2003},
url = {http://www.jstor.org/stable/3647851},
researchr = {https://researchr.org/publication/HavlicekW03},
cites = {0},
citedby = {0},
journal = {The American Mathematical Monthly},
volume = {110},
number = {8},
pages = {679-693},
}