Education Technology

Triangle Inequality Theorem

Activity Overview

In this activity, students will explore the concepts underlying the Triangle Inequality Theorem by comparing side lengths and angle measures of a triangle. They will use an interactive construction to see why this theorem is true.

Before the Activity

  • Install the Cabri Jr. App on the students' graphing calculators using TI Connect™, a TI Connectivity Cable and the Unit-to-Unit Link Cable
  • Use the TI-Navigator™ to transfer the attached Cabri Jr. AppVar files to each calculator
  • See the attached PDF file for detailed instructions for this activity
  • Print pages 91 - 93 from the attached PDF file for your class
  • During the Activity

    Distribute the pages to your class.

    Follow the Activity procedures:

  • Use the AppVar to go directly to the exploration section
  • Draw a triangle and measure its angles and sides
  • Observe the relationship between the angle measures and the length of the side opposite the angle
  • Construct a special triangle with its first vertex as the center of a circle, its second vertex as a point within the circle, and its third vertex as a point on the circle
  • Observe the relationship among the three sides of a triangle
  • After the Activity

    Review student results:

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