(no subject)

[keaki83]

Materials:        A rectangular wooden box containing the following 14 triangles:

·        Two green right-angled isosceles triangles, each with a black line on the hypotenuse of each triangle

·        Two gray right-angled scalene triangles, each with a black line on the hypotenuse

·        Two yellow equilateral triangles, each with a black line on one side

·        Two yellow right-angled isosceles triangles (equal to the green above), each with a black line on one of the sides enclosing the right angle

·        Two yellow right-angled scalene triangles (equal to the gray above), each with a black line on one of the side enclosing the right angle

·        Two green right-angled scalene triangles (equal to the yellow and gray above), with black lines on the longer of the two sides enclosing the right angle

·        One red right-angled scalene triangle with a black line on the longer of the two sides enclosing the right angle

·        One red obtuse-angled scalene triangle with a black line on the side opposite the obtuse angle

Each pair has the black line on the corresponding sides. These black lines are the lines by which the triangles will be joined together.

Note: The material is called “constructive” because the triangle is used to form other rectilinear figures.

Prerequisites:  Geometry Cabinet, language for the Geometry Cabinet

Presentation:

1. Invite child for an individual lesson
2. Ask, “Do you know what “construct” means?”
3. Take out two right-angled scalene, and two yellow equilateral triangles, and two green right-angled isosceles triangles. Scatter them on the mat.
4. Take out one of the green, and say “Can you find one of the same size, shape and color?”
5. Show how to superimpose. Then show how to match black lines together, keeping the left one steady.
6. Ask, “What does this make?”
7. Repeat steps 4-6 for gray triangles, matching the black lines to form a rectangle.
8. Repeat again for yellow equilaterals to form a rhombus.
9. Then take out two yellow right-angled isosceles triangles and two yellow right-angled scalene triangles, and green right-angled scalene.
10. Work with these three in the same way-superimpose, then match the black lines. These three all form parallelograms.
11. Take out the two red triangles. The child will see that they cannot be superimposed. “But since these are the same color, we’ll keep them together.”
12. Match the black lines to form a trapezoid.
13. Invite the child to repeat.

Order to put away:

1. Put two red triangles in form of trapezoid on the left-hand side of the box
2. Two large yellow right-angled isosceles in a square to the right (black lines won’t match)
3. Two smaller green triangles on the left, making a rectangle.
4. Two large green on right making a square
5. Two yellow right-angled scalene on left, making a rectangle
6. Gray on left forming rectangle
7. Two yellow equilaterals on right, forming a rhombus

Control of Error: Mechanical and perceptual-black lines correspond to make the figures

Direct Aim: To show that quadrilaterals are formed by joining two triangles

Indirect Aim:   To show that all plane geometric forms that are constructed of straight lines are

composed of triangles; indirect preparation for finding area and equivalence of different shapes

Age: 4-5

Language: Superimpose