Education Technology

Move Along Little Vertex

Published on 06/09/2008

Activity Overview

In this activity, students use the Geoboard to determine the area of triangles having the same base and same height.

Before the Activity

  • Start the Geoboard App and format it
  • See the attached PDF file for detailed instructions for this activity
  • Print pages 21 - 31 from the attached PDF file for your class
  • During the Activity

    Distribute the page to the class.

    Follow the Activity procedures:

  • Construct two parallel line segments
  • Between these two parallel lines build three different triangles, each with the same base and same height
  • Use the calculator to find and record the area of each triangle
  • Observe they have the same area
  • Note that moving a vertex of a triangle along a line that is parallel to the triangle's base does not change the triangle's height nor its area
  • Observe that shifting a triangle's vertex between parallel lines can change any triangle into a right triangle with the same area


  • Draw a diagonal and redesign the quadrilateral using triangles between parallel lines
  • Calculate the area of the triangle formed and thus the area of the quadrilateral


  • Using triangles between parallel lines move one vertex so that a pentagon changes to a quadrilateral with the same area


  • Solve word problems to measure area of geometric figures using triangles between parallel lines
  • After the Activity

    Students complete the Activity sheet and answer questions.

    Review student results:

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