Click the
red button ()
on the figure below to start the animation. Drag points A, B, D,
and F, and line AF to change the figure. Press P and click the left mouse button to start the step by step
construction, help.

Proposition
The orthocenters of the four triangles
(BCE, CDF, ABF, ADE) of a complete quadrilateral ABCDEF lie on a
line called Ortholine - Steiner Line.

Complete quadrilateral ABCDEF is the figure determined by
four lines, no three of which are concurrent, and their six
points of intersection A, B, D, C, E, and F.

The orthocenter is the intersection of the three altitudes of a triangle. Post a comment.

Dynamic Geometry: You can alter the figure
dynamically in order to test and prove (or disproved)
conjectures and gain mathematical insight that is less
readily available with static drawings by hand.

This page uses the
TracenPoche
dynamic geometry software and requires
Adobe Flash player 7 or higher.
TracenPoche is a project of Sesamath, an association of French
teachers of mathematics.

Instruction to explore the
dynamic figure:

Animation. Click the red
button
to start/stop animation

Manipulate. Drag points A,
B, D, and F, and line AF to
change the figure.

Step-by-Step construction.
Press P and click the left mouse
button
on any free area of the figure
above to show the
step-by-step bar and click 'Next
Step' button ()
to start the construction step-by-step:

Hide the step-by-step bar by
using again the combination P +
click left mouse.