Enlargements create shapes that are similar. To understand congruence and similarity, a good understanding of the properties of polygons, including triangles and quadrilaterals, can be helpful.

Sketch 1 is intended to help the students attend to the similarities and differences between the three triangles. While initially very similar looking, these triangles behave very differently under ...

Or the Animate feature to display families of triangles. Have the students notice that the triangle always has three sides. Have the students draw triangles using pencil and paper. Ask for examples of ...