After studying angles and classifying figures, we come back to sorting triangles. I built them according to angle (first row) and then according to length of the sides(second row).
Although I did not describe it in detail, building in this way reflects how we began to study the angles and lines. We’ve discovered that the first figure (polygon) that we can build with the sticks is the triangle.
But how many kinds of triangles are there? What are the relationships between lengths of the side? That is what we are setting out to discover….We come up with these six.



But what about a right-angled scalene triangle? This comes with a story!
(Everything in early Elementary comes with a story.)
This string is like the strings of the ancient Egyptian surveyors. They were interested in making right angles so they could build pyramids and mark out plots of land, especially after the Nile flooded the farm land. They found that they could be very sure of a right angle if they had this special sort of triangle, easily measured by rope: three knots on one side, four on the other, and five across.
All we say now is ‘Hmmm!’ The children are ready for more adventures, but let’s not spoil the surprise!

There is still more to discover: here, finding the height of a triangle. Even though we’re measuring against an acute scalene, what would happen if we measured the others in the same way? What will we see with the obtuse triangles? (For example!)

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