Education Technology

Move Along Little Vertex

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