CONSTRUCTIVE TRIANGLES

The materials of the Constructive Triangles help the child consolidate into her conscious understanding shape, size (dimension) and colours and help her to realise that the triangle has the roles of a constructor, divisor and consequence. The child first needs to be aware of shape and size and familiar with the names presented in the ‘Three Period Lesson’ accompanying the Geometric Cabinet, so that she can verbally express her ideas. The triangles are called ‘constructive’ because they construct other rectilinear shapes.

Material Description
Five boxes of coloured wooden triangles:

Two rectangular boxes
One triangular box
One large hexagonal box
One small hexagonal box

Two yellow isosceles right-angles triangles with a black line painted on one of the sides enclosing the right angle
Two green isosceles right-angles triangles equal to the yellow ones, with a black line painted on the hypotenuse of each
Two yellow scalene right-angles triangles with a black line painted on the shorter of the two sides enclosing the right angle
Two green scalene right-angles, equal to the yellow scalene, with black lines painted on the longer of the two sides enclosing the right angle
Two grey scalene right-angles triangles, the same size as the scalene triangles with a black line painted on the hypotenuse
Two yellow equilateral triangles, with black lines on one side
One red scalene right-angled triangle with a black line painted on one of the sides enclosing the right angle
One red scalene obtuse-angled triangle with a black line painted on the the side opposite the obtuse angle.

Exercise
After the children have experienced working with each of the Constructive Triangle Boxes, they may combine the boxes to create new shapes using many different types and shape of a triangle. To put away the triangles the children are guided by colour dots on the back of the triangles and the lids of the boxes.

Direct Aim
To show that by joining together different triangles quadrilaterals are formed
To help the child discover the function of a triangle as a constructor.

Indirect Aim
Preparation for Geometry: to show that rectilinear plane figures are composed of triangles
Preparation for understanding the concept of equivalence and it’s application in finding the area of plane figures
To help the child prepare herself to identify equilibriums that are; identical, similar and different
To look at comparative figures
To prepare for fractions.