# Activities

• • • ##### Subject Area

• Math: Geometry: Triangles

• ##### Author 6-8

30 Minutes

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

TI Connect™

• ##### Accessories

TI Connectivity Cable

• ##### Other Materials
The following equipment is required for this activity:
• TI-Presenter™

• LCD Projector
• Two screens

## Dynamic Geometry: Program Basics

#### Activity Overview

Students use the Cabri™ Jr. application to draw triangles and explore properties of perpendicular bisectors of the three sides of different types of the triangles. They study the measures of angles of a triangle and understand that the sum of the measures of angles of a triangle is always 180 degrees.

#### 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 1 - 19 from the attached PDF file for your class
• #### During the Activity

Distribute the pages to the class.

• Explore the tools and submenus accessed through the function keys
• Construct a triangle and label its vertices
• Measure the angles of the triangle
• Construct three perpendicular bisectors on each of the sides of the triangle
• Determine the point of intersection of the perpendicular bisectors
• Hide the perpendicular bisectors and display only the intersection point
• Make conjectures about the intersection of the perpendicular bisectors of a triangle when the triangle is acute, right, or obtuse
• Draw a triangle and measure the angles
• Calculate the sum of the angle measures and observe that it is 180 degrees
• Move a vertex around the screen and observe that the sum does not change
• #### After the Activity

Review student results:

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