As an
introduction to our Geometry unit, our class explored "The Four Triangle
Problem". This puzzle introduces students to geometric concepts and
vocabulary, provides experience sorting and classifying polygons, and develops
spatial reasoning and flexible thinking.

Before
the lesson, I made triangles by folding and cutting post-it notes in
half on the diagonal. Each group of students were asked to
make as many shapes as they could by joining first two paper triangles with the result: triangle, parallelogram and a square and then the next day four paper triangles. They were told that they must meet together edge
to edge, with the rule that touching sides must be the same length and
match exactly. I had students first draw the shapes in their math journals and then tape
together the triangles. We classified the shapes we made on a classroom chart labeling the different polygons (triangle, quadrilateral, pentagon and hexagon) by counting the number of sides and angles.

We charted all of the possible polygons. There are 14 in all! Google, The Four Triangle Problem by Marilyn Burns to view the complete less

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