Dynamic Geometry 1448: Simson Line

Given a triangle ABC and a point D on its circumcircle, then the feet H,F,E of the perpendiculars drawn from D to the sides (or their extensions) are collinear. The line HFE is called the Simson line of D.

Robert Simson (1687 - 1768) was a Scottish mathematician and professor of mathematics at the University of Glasgow.


Static Diagram of the Simson Line of a triangle

Geometry Problem 1448: Simson Line. Using GeoGebra


Poster of the Simson Line using iPad Apps

Poster of The Simson Line Dynamic Geometry. Using iPad

Classroom Resource:
Interactive step-by-step animation using GeoGebra

This step-by-step interactive illustration was created with GeoGebra.

  • To explore (show / hide): click/tap a check box.
  • To stop/play the animation: click/tap the icon in the lower left corner.
  • To go to first step: click/tap the "Go to step 1" button.
  • To manipulate the interactive figure: click/tap and drag the blue points or figures.

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