The Journal of Online Mathematics and Its Applications, Volume 7 (2007)
GeoGebra, Markus Hohenwarter and Judith Preiner

Triangle Constructions

Using GeoGebra like a DGS we constructed a triangle for given sides a, b and c with the tools "Segment with given length" and "Circle with center and radius". Click the forward button Button: Fast Forwardin the navigation bar to go through the construction step by step. Use the sliders to investigate whether this Side-Side-Side (SSS) construction is possible for any given lengths a, b and c.

Sorry, the GeoGebra Applet could not be started. Please make sure that Java 1.4.2 (or later) is installed and activated. (click here to install Java now)

Editor's note, May 2014: For an HTML5 version of the above applet, click here.

Here is the construction protocol of a triangle for three given side lenghts (SSS):

The advantage of this DGS construction compared to one on paper is that you can vary the side lengths of the triangle dynamically. By changing the three sliders a, b and c we are able to examine a multitude of different triangles. Doing so, your students can easily find out that it's not always possible to construct a triangle for given side lengths. This observation can be the starting point for an interesting discussion about the triangle inequality.