Education Technology

Dynamic Geometry: Program Basics

Published on 06/09/2008

Activity Overview

Students use the Cabri™ Jr. application to draw triangles and explore properties of perpendicular bisectors of the three sides of different types of the triangles. They study the measures of angles of a triangle and understand that the sum of the measures of angles of a triangle is always 180 degrees.

Before the Activity

Install the Cabri: Jr. App on the students' graphing calculators using one of these two methods:

  • TI-Connect™,  a TI Connectivity Cable, and the Unit-to-Unit Link Cable
  • TI-Navigator™  "send to class" feature
  • See the attached PDF file for detailed instructions for this activity
  • Print pages 1 - 19 from the attached PDF file for your class
  • During the Activity

    Distribute the pages to the class.

    Follow the Activity procedures:

  • Explore the tools and submenus accessed through the function keys
  • Construct a triangle and label its vertices
  • Measure the angles of the triangle
  • Construct three perpendicular bisectors on each of the sides of the triangle
  • Determine the point of intersection of the perpendicular bisectors
  • Hide the perpendicular bisectors and display only the intersection point
  • Make conjectures about the intersection of the perpendicular bisectors of a triangle when the triangle is acute, right, or obtuse
  • Draw a triangle and measure the angles
  • Calculate the sum of the angle measures and observe that it is 180 degrees
  • Move a vertex around the screen and observe that the sum does not change
  • After the Activity

    Review student results:

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