Sample Lesson

From the book: Geometry and Number

Discover the Triangles

Lesson Activity: Discover the Triangles

In this lesson the student will see that three intersecting lines will create a triangle. The result is an artistic representation of various kinds of triangles that has a quality reminiscent of some modernist paintings.

Begin by drawing random lines across the width and length of the paper, moving horizontally, vertically and diagonally. The student can us the straight edge for this. At least a dozen lines should be drawn; more than two dozen lines will create too many intersections. Now find different triangles and color them with the color pencils.

Lead the student to find the basic kinds of triangles: In addition to the triangles shown in the illustrations, there are also: the right triangle (we will study this in the next lesson), the acute triangle (each of the interior angles are less than 90 degrees) and the obtuse triangle (one of the interior angles is more than 90 degrees). At this point we do not need to pull out the protractor and measure angles; we are simply bringing the various types to the student's attention. In the main lesson book on the page adjacent to the artistic rendering, have the student freehand draw the six types of triangles and label them. The teacher should draw these on the blackboard or a sheet of paper while explaining the qualities that differentiate each and the student will then draw the same in the main lesson book.