This dynamic 3D applet does not work on Internet Explorer, and works best on a relatively new version of the free browser Firefox - click link to download latest version. It also requires the downloading & installation of the free Cabri 3D Plug In, available at Windows (4 Mb) or Mac OS (13.4 Mb).
Basic manipulation: 1) Right click (or Ctrl + click) and drag to rotate the whole figure (glassball).
2) Click to select and hold down the left button to drag any of the four vertices of the tetrahedron.
Or click Summary of manipulation to open & resize a separate window with instructions.
The altitude of a tetrahedron is the analogue of an altitude of a triangle in the plane. Hence, since an altitude of a triangle is a perpendicular to an opposite side, a median of a tetrahedron is the perpendicular from a vertex to an opposite face.
Important Note: Though one may expect the four altitudes of a tetrahedron to also always be concurrent like those of the perpendicular edge bisectors, face angle bisectors and medians, the altitudes in contrast are not necessarily concurrent, as can be seen above.
Read more at 3D Concurrency Counter-example.
HTML export by Cabri 3D. Download a 30 day Demo, or for more information about purchasing this software, go to Cabri 3D.
Created by Michael de Villiers, 27 April 2012; updated 20 April 2024.