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Activity Overview

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

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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
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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
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After the Activity

Review student results:

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