[1] A. Pllana, Miscellaneous Results on Tetrahedron.
http://mathforum.org/MiscTetra2.pdf
[2] Einar Hille, Analytic Function Theory, Volume I, Second Edition,
Fifth Printing, Chelsea Publishing Company, New York, 1982, ISBN
0-8284-0269-8, page 33.
[3] A. Altıntaş, Some collinearrities in heptagonal triangle, Forum
Geometricorum 16 (2016).
[4] P. Yiu, Introduction to Geometry of Triangle, Florida Atlantic
University, 2002.
[5] J. Sadek, M. Bani and H. N. Rhee, Isogonal conjugates in
tetrahedron, Forum Geometricorum 16 (2016).
[6] Nairi M. Sedrakyan, Another look at the Volume of a Tetrahedron,
Canadian Mathematical Society 27 (2001), 246-247.