Constructive Triangles: Second Box: Trapezoid

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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)



  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.
  8. The quadrilateral is called a common quadrilateral.
  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.

Control Of Error

Points Of Interest


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



Constructive Triangles Boxes # 1-5