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4 A typical task in interactive geometry could be "Construct a square", with this solution: 1. Construct two points, A and B, and a line through them. 2. Construct lines through both points perpendicular to that line. 3. Measure the distance AB and transfer that distance to the two perpendicular lines, measured from A and B. This constructs two further points C and D. 4. The square ABCD is constructed. One problem: It is harder to learn these skills than it is to learn what a square is.

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Figure 1: Geometer's Sketchpad

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Figure 2: JavaSketchpad - drag the red points

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Figure 3: Cinderella

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Figure 4: a Cinderella exercise

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Figure 5: a Cinderella exercise

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5 Summary On-line dynamic geometry meets 3 of our 4 criteria. technology no technological knowledge required by user design it is clear what has to be done; minimal explanation needed development software available to teachers, curriculum designers and web authors to develop content further For content see: Transformations (Mathplets 2000): at FreeCampus | at MathsNet Construction: at MathsNet Shape: at MathsNet and MathsNet's Cinderella section. Cabri, perhaps the first dynamic geometric software, also has a web development at Cabri-Geometre .