Education Technology


Published on 06/09/2008

Activity Overview

Students use the Cabri Geometry II Plus software to investigate the geometric property of dilation. They vary the scale factor and examine the effect on the dilation of a triangle.

Before the Activity

  • Download the Cabri Geometry™ software on the computer

  • See the attached FIG file for details of this activity

  • During the Activity

    Follow the Activity procedure:

  • Move Point K along the line
  • Note that for positive values of K, the triangle maintains its shape, but changes its size with respect to point O
  • Note that for K = 1, the two triangles coincide
  • Note that for K = 0, the dilated triangle coincides with point O
  • Observe that for negative values of the scale factor K, the dilated image gets inverted, and increases in size as the K value decreases
  • Understand that at K = 0.50, the sides of the dilated triangle will be half the length of sides of the original triangle, while the angles remain same
  • After the Activity

    Review student results:

  • As a class, discuss questions that appeared to be more challenging
  • Re-teach concepts as necessary