To further the child’s exploration with equilateral triangles.
Preparation for geometry: to show that all plane figures constructed with straight lines are composed of triangles.
Extending the understanding for the concept of equivalence and its application for finding the area of plane figures.
The black lines.
4 – 5 years
 Two red equilateral triangles with a black line along one side
 Three green equilateral triangles with black lines:
One along two sides
Two along one side
 Six gray equilateral triangles with black lines long two sides
Invite the child by telling him you have something to show him. Bring him over to the correct shelves. Show the child clearly that you are choosing the small hexagonal box. Have him carry it to the table and have him place it near the top right corner of the table. Have the child sit to your left, and then you sit down.
 Remove the lid of the box using both hands.
 Place the lid directly in front of the box and place the box on top of the lid.
 Take out all of the triangles.
 Place them randomly to the left of the box.
 Move the box above the lid and then replace the lid on the box.
 Slide the rhombus up to the top left corner of the table.
 Using the black lines as a guide, create a trapezoid with the three green triangles.
 Slide the trapezoid up to the right of the rhombus.
 Then build a hexagon with the six gray triangles.
 Slowly and gently remove two of the gray triangles to form a rhombus.
 Slide it under the red trapezoid to shoe the similarity.
 Repeat for the other two pairs, thus creating three gray rhombi.
 Place them both under the red rhombus.
 Replace the gray triangles together to create the hexagon.
 Slowly remove the top three triangles to create a trapezoid.
 Slide it under the green trapezoid to show the similarity.
 Rotate the bottom three triangles to create an upright trapezoid and place it
under the red and gray trapezoid.
 Mix up all of the triangles and allow the child to build the shapes.
 Once the child is done, show him how to put all of the triangles back into the
box: first put all of the gray triangles back, then place the red triangles back,
and finally the green triangles.
As the child has been taught the names with the geometry cabinet, there is no language lesson given with this material.
