http://www.math.washington.edu/~king/coursedir/m444a02/lab/lab10.html

http://www.math.washington.edu/~king/coursedir/m444a04/class/class29.html

http://www.math.washington.edu/~king/coursedir/m444a04/notes/orthic/www/Altitudes%20and%20Orthic%20Tri.htm

http://www.math.washington.edu/~king/coursedir/m445w05/as/projects/FERMAT%20POINTQuest.html

http://faculty.evansville.edu/ck6/tcenters/class/fermat.html

http://www.math.washington.edu/~king/coursedir/m444a03/wk10.html

http://www.math.washington.edu/~king/coursedir/m444a03/notes/12-05-Napoleon-Fermat.html

http://mathworld.wolfram.com/OrthicTriangle.html

http://faculty.evansville.edu/ck6/tcenters/