Triangles

Age

6-9.

Materials

• Reading labels - "scalene triangle", "isosceles triangle", "equilateral triangle", "right-angled triangle", "obtuse- angled triangle", "acute-angled triangle"
  

Presentation

1. Take out the first triangle in the first row.
2. Invite the child to identify the three sides and observe whether the sides are alike or different.
3. All three sides are different, this is a scalene triangle.
4. Relate the story of the farmer and the ladder he used to pick fruit from his trees.
5. Unlike the ladders we use today, the rungs of this ladder were all different lengths.
6. These ladders are still used today in lesser developed countries.
7. Just as all the rungs are different lengths, the sides of this triangle are all different lengths (scalene: Latin scala, usually plural scalae - ladder, flight of steps or Greek: skalenas - limping, uneven).
8. Isolate the second triangle in the first row.
9. Invite the child to carefully observe its sides - two are alike.
10. This is an isosceles triangle (isosceles: Greek isos - equal, and sceles - legs; thus having equal legs).
11. Here it means two equal legs, or sides.
12. Isolate the third triangle.
13. By observing and turning the inset in its frame, the child sees that all of the sides are the same.
14. This is an equilateral triangle (equilateral: Latin aequus - equal, and latus, lateris - a side; thus having equal sides).
15. Place the three insets on the table and do a three period lesson.
16. Isolate the first triangle in the second row.
17. Identify the right angle.
18. This is a right angle, it is erect.
19. This is a right-angled triangle.
20.  How many right angles does it have? Only one.
21. Isolate the second triangle.
22. Identify the obtuse angle.
23. Obtuse means dull.
24. This is an obtuse-angled triangle.
25. Count the obtuse angles... only one.
26. Isolate the third triangle.
27. All of these angles are smaller than the right angle.
28. They are acute angles.
29. Acute means sharp, pointed.
30. Feel how it is sharper than the right or obtuse angles.
31. This is an acute-angled triangle.
32. How many acute angles does it have? Three.
33. Bring out the three triangles and review the first period.
34. The triangle must have one right angle to be a right-angled triangle... and so on.
35. Second and third periods follow.
36. Give the child the reading labels.