Stage: 3 Challenge Level: 
You need to be systematic. Start with certain limitations (constraints) and exhaust all possibilities - try to justfy how you know there are no other triangles in this "category". Then extend your investigation to more categories.
Compound transformations. Mathematical reasoning & proof. smartphone. Congruence. Generalising. Cubes. Mixed triangles. Interactivities. Working systematically. Visualising.
Published November 2002,December 2002.
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