# Constructive Triangles: Second Box: Trapezoid

## Contents

6-9.

### Materials

Box 2 -

• Two blue equilateral triangles
• Two blue right-angled isosceles triangles
• Two blue right-angled scalene triangles
• One blue obtuse-angled scalene triangle
• One blue right-angled scalene triangle (corresponds to the red triangle from Box 1)

### Presentation

1. With the two small red triangles, invite the child to unite the triangles along the black lines and identify the figure obtained - a trapezoid.
2. Using the two corresponding blue triangles, invite the child to form the figure which he already knows and to identify it - a trapezoid.
3. Continue making other quadrilaterals using only the obverse sides.
4. The directress identifies the figure obtained.
5. Since it has four sides we can call it a quadrilateral.
6. It is a concave quadrilateral - a boomerang (it may also be called a re-entrant).
7. Invite the child to turn over one triangle to form any other figures, quadrilaterals or triangles.
9. The triangle is an obtuse-angled isosceles triangle.
10. Note: This triangle has great importance in the later study of the area of a trapezoid.
11. Recall the figures formed by these triangles; there are four.

### Purpose

• Exploration of the triangle as the constructor of triangles and quadrilaterals.