Cabri Geometry II Plus review

Dynamic probably isn't a word you'd have associated with your secondary-school maths teacher.

But that's how Cabri's Geometry tutor describes itself. And this handy bit of software isn't content to be left in the classroom - it aims to become part of the toolkit of any working mathematician.

Dynamic geometry programs let you build geometric constructions on-screen as you would with a ruler and compass. But they differ from computer-aided design programs in that they're not meant for making precise technical drawings. Instead, they allow you to manipulate a diagram in order to investigate the properties of a figure through experimentation, and check out possible theorems. For instance, you can test whether it's true that the perpendicular bisectors of a triangle meet in a single point - the centre of the circle passing through all three vertices.

Cabri Geometry II Plus is easy to get to grips with. To draw a line segment, for example, you just choose the Segment command and select two end points on the screen.

Among the many objects Cabri lets you draw are points, lines, polygons, circles and sections through cones (that's parabolas, ellipses and hyperbolas, for the initiated). You can bisect lines and angles, draw perpendicular and parallel lines and produce loci. All objects can be transformed and measured, so you can test out mathematical rules. There's a macro facility for saving more complicated constructions of your own, and adding them as new commands. And when you've finished, you can publish interactive diagrams on the Web.

Things are often much easier to figure out with a diagram, so Cabri's usefulness extends way beyond academia. However, younger children will need guidance. Cabri's distributor, Chartwell-Yorke, offers a book on using the software at Key Stage 3, and a CD-ROM with Cabri files and associated lessons for up to GCSE level. Cabri is a fine tool for students, teachers, researchers and maths enthusiasts. With careful use, it can turn geometry into an enjoyable hands-on pastime.