# Activities

• • • ##### Subject Area

• Math: Geometry: Circles

• ##### Author 6-8

60 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

## Coordinate Geometry - Circles

#### Activity Overview

In this activity, students investigate the relationship between the coordinates of a point on the circle, radius of a circle, and the values in the equation of the circle.

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

Distribute the pages to the class.

• Drag the circle so that the center of the circle is at the origin
• Display the coordinates of point P, where the circle intersects the x-axis
• Display the coordinates of the center and the equation of the circle
• Notice that the x-value of P represents the radius of the circle
• Drag point P along the x-axis and relate the equation of the circle to the coordinates of point P
• Move the center of the circle away from the origin
• Observe the coordinates of the center and point P
• Observe how the values relate to the equation of the circle
• #### After the Activity

Review student results:

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