Education Technology

Extension: Parallel Lines and the Sum of the Angles

Published on 06/09/2008

Activity Overview

Students construct a line parallel to the base of a triangle and measure the angles formed. They use the construction to prove that the sum of the measures of the interior angles of a triangle is 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 - 4 from the attached PDF file for your class
  • During the Activity

    Distribute the pages to the class.

    Follow the Activity procedures:

  • Draw a line parallel to the base of a triangle through the top vertex
  • Measure the angles that are formed by the parallel line and the sides of the triangle
  • Measure the interior angles of the triangle
  • Use the figure to prove that the sum of the interior angles of any triangle is 180 degrees
  • After the Activity

    Review student results:

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