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'Inside Triangles' printed from http://nrich.maths.org/
Here is a four by four dotty grid:
I have joined three dots on the grid to make a triangle which has one dot inside it:
How many different triangles with one dot in the middle can you draw?
How do you know have found them all?
You may like to experiment with the pegboard interactivity below, or you could print off this page of dotty grids to work on.
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