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Constructive Triangles, Rectangular Box 2

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The triangles correspond to those in Box 1. (one of each type)
They are blue with no black lines.  
1 pair right-angled isosceles triangles.  
1 pair right-angled scalene triangles.  
1 pair equilateral triangles.  
1 right-angled scalene triangle.  
1 obtuse-angled scalene triangle.  


  1. Invite the child to the lesson. 
  2. Take out a triangle and place it on the rug.  
  3. Take out its corresponding triangle and place it next to the other one. 
  4. Place one triangle on top of the other one.  
  5. Take a moment to examine their size.  
  6. Take the triangle off and place it back next to the other one. 
  7. Bring the pair together. 
  8. Hold a triangle still with your left hand. 
  9. With your right hand on the other triangle, slowly slide the triangle clockwise along the edge until two points meet.  
  10. With your right hand, slide the triangle to the right. 
  11. Examine the new shape that was formed.  
  12. Ask the child if he knows the name of the shape.   
  13. Slowly slide the triangle along the edge until two new points meet. 
  14. Slide the triangle up along the edge. 
  15. Examine the new shape that was formed. 
  16. Slowly slide the triangle up along the edge until two new points meet.  
  17. Slide the triangle to the left. 
  18. Slide the triangle down, forming its original shape. 
  19. Invite the child to remove one new pair of triangles, until he has worked with them all.


Exercise 1: Child works independently.
Exercise 2: Flip Over
Flip over one triangle of each pair and let the child explore them.



Control of Error


Direct Purpose

To show the child that joining two triangles forms a single straight lined figure.

Indirect Purpose

Preparation for understanding equivalence.
To see how all plain geometric figures constructed of straight lines are composed of triangles.


4 to 5


Same shapes as in Box 1, except they are all blue and have no black lines.
We are gradually moving towards an understanding of equivalence.

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