How Does This Button Work?

Chris Sangwin

Author Information

Christopher J. Sangwin is a lecturer in the School of Mathematics at the University of Birmingham, UK. You may contact him by e-mail, or visit his website for more information about his projects and research interests.


It is not clear at the outset in dynamic geometry how the buttons relate to each other, or that the possibility of catastrophic circularity can be avoided. This was something previous writes such as Euclid were at pains to avoid. Hence we ask "how does this button work?". Or, put another way, this article is one attempt to examine the dynamic geometry package GeoGebra from the point of view of Euclidean Constructions.

Technologies Used in This Article

  • This article uses Java (1.4.2 or later) for several interactive applets created with GeoGebra. You may need to install or upgrade the Java plug-in.
  • The article has two video clips in the QuickTime Video (.mov) format. You may need to install the QuickTime Player to view these videos.
  • The following HTML symbols are used: minus −, prime ′. If these do not display, you may need to upgrade your browser.


  • GeoGebra
  • Euclidean construction
  • geometry

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