Education Technology

# Activities

• ##### Subject Area

• Math: Geometry: Triangles

9-12

20 Minutes

• ##### Software

Cabri Geometry™

## Dilation

#### 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

• See the attached FIG file for details of this activity

• #### During the Activity

• 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