Some years ago, I started using interactive geometry software. My application of choice was Cabri, because I appreciated its mathematical depth and the elegant simplicity of its interface. I developed a number of Cabri-based activities, many of which you can find on my Web site. For example:

(There are more. Find them here.)

Later, I started working with Cabri 3D, a beautiful extension of interactive geometry to the third dimension. You can see some of the resulting work on the site (3D geometry of the parabola and ellipse.)

At this point, Cabri 3D faces no competition. Yes, CAS software can graph in three dimensions, but that is not geometry in the same sense. Google’s SketchUp is great at what it does, and probably can find some great uses in the classroom, but again, it is not geared to geometry. For example, try to create a regular dodecahedron with that software. It’s possible, but there is just no comparison with Cabri 3D where the dodecahedron is provided as one of the tools, and where building one from more basic tools makes for a challenging and accessible lesson. I enthusiastically recommend this application.

On the other hand, there are many alternatives to Cabri in two dimensions. Geometer’s Sketchpad was the main option for a long time, and there are many others. A more recent entrant in this field is GeoGebra, which is open source and free. Its design is largely inspired by Cabri, but it goes further, offering CAS, an elementary spreadsheet, graphs as first class objects, an input line, and more. Because it is available for free, it has dealt a near-fatal blow to both Cabri and Sketchpad. Both of these programs have aspects that are superior to GeoGebra, and have made gigantic contributions to the intelligent use of computers in the math classroom, but I’m afraid they are not able to compete with free.

Because of all this, I have decided to learn GeoGebra, and to post my creations on this site. This will include some activities that use the graphing calculator and some that use interactive geometry. To get this started, I have updated some pages and edited or added some worksheets:

- Rolling Dice
- Graphing Square Roots
- Proof in High School Geometry
- Letters and Postcards (interactive graph)

I have also revised my construction unit to make it easier to use with any interactive geometry software, including GeoGebra.

If you want to keep up with my GeoGebra creations, please subscribe to this blog (look to the right!) I will make sure to announce the new additions here.

–Henri