Education Technology

Similar Figures

Activity Overview

In this activity, students investigate the properties of similar triangles.

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 53 - 55 from the attached PDF file for your class
  • During the Activity

    Distribute the pages to the class.

    Follow the Activity procedures:

  • Construct a triangle and label it ABC
  • Use the Dilation feature in the calculator to construct a similar (same shape, different size) triangle DEF
  • Measure the lengths of the sides of the two triangles and tabulate them
  • Calculate the ratio of the length of a side of one triangle to the length of the corresponding side of the other triangle
  • Calculate the ratios for the remaining sides
  • Observe that the ratios of the corresponding sides are congruent
  • Alter the triangles and verify the observation
  • Notice that for similar triangles, the lengths of the corresponding sides are proportional
  • Find the perimeter of the two triangles and calculate the ratio
  • Note that the ratio of the perimeters of two similar triangles is equal to the ratio of the proportional sides
  • Measure the corresponding angles of the two triangles
  • Note that the corresponding angles of similar triangles are congruent
  • Alter the triangles and verify the relationship
  • Note that a polygon with more than three sides also shows a similar relationship
  • After the Activity

    Review student results:

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