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'Nine-pin Triangles' printed from http://nrich.maths.org/

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How many different triangles can you make on a circular pegboard that has nine pegs?

You may like to use the interactivity to try out your ideas. If you prefer to work on paper, you might find this sheet of nine-peg boards useful.

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Once you've done this, have a look here for some extension questions!

Many thanks to Geoff Faux who introduced us to the merits of the nine-pin circular geoboard.
The boards, moulded in crystal clear ABS that can be used on an OHP (185 cm in diameter), together with a teacher's guide, are available from Geoff at Education Initiatives