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.

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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.