# Activities

• • • ##### Subject Area

• Math: Geometry: Similarity and Proportion

• ##### Author 9-12

60 Minutes

• ##### Device
• TI-83 Plus Family
• TI-84 Plus
• TI-84 Plus Silver Edition
• ##### Software

Cabri Geometry™
TI Connect™

• ##### Accessories

TI Connectivity Cable

• ##### Other Materials
This is Activity 13 from the EXPLORATIONS Book:
Exploring The Basics Of Geometry With Cabri

## 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.

• 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