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Bisectors

Activity Overview

Students investigate the Perpendicular Bisector Theorem and examine its converse. They also explore the Angle Bisector Theorem.

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 17 - 21 from the attached PDF file for your class

    • During the Activity

    Distribute the pages to the class.

    Follow the Activity procedures:

  • Draw a segment AB and construct its perpendicular bisector
  • Label the point of intersection of segment AB and the perpendicular bisector as C
  • Construct point D on the perpendicular bisector
  • Measure and record the lengths of AD and BD
  • Drag point D along the line and measure the lengths of AD and BD
  • Observe that the lengths od AD and BD remain equal for any position of point D
  • Observe that any point on the perpendicular bisector of a segment is equidistant from the endpoints of the segment
  • Identify that the triangle formed by points A, B, and D is an isosceles triangle


  • Construct a segment AB
  • Measure the length of segment AB
  • With the same measure, create a segment AC
  • Connect points B and C to form an isosceles triangle
  • Move the vertex A and observe that point A is equidistant from point B and point C
  • Construct a perpendicular bisector of segment BC
  • Observe that point A lies on the perpendicular bisector of segment BC
  • Drag point A along the perpendicular bisector to verify the observation that a point which is equidistant from the endpoints of a segment, lies on its perpendicular bisector


  • Draw an angle and construct its angle bisector
  • Construct a point on the bisector in the interior of the angle
  • Measure the distance from this point to the rays of the angle
  • Identify that the distance from the point to each ray is equal
  • Drag the point along the bisector to verify this observation
  • Understand that a point that lies on the angle bisector of an angle, is equidistant from the sides of the angle

    • After the Activity

    Review student results:

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

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