Go Geometry: Archimedes Arbelos and Square

Complete Quadrilateral: Ortholine-Steiner Line. Interactive Geometry Software

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.


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:

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


Complete quadrilateral



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