# Activities

• • • ##### Subject Area

• Math: Geometry: Circles

• ##### Author 6-8

60 Minutes

• ##### Device
• TI-73 Explorer™
• ##### Other Materials
This is Activity 11 from the EXPLORATIONS Book:
Shaping Middle Grades Mathematics: Activities for Geoboard and the TI-73

3.14159265...

#### Activity Overview

In this activity, students investigate the circumference of circles and learn about the irrational number Pi.

#### Before the Activity

• Start the Geoboard App and format it
• See the attached PDF file for detailed instructions for this activity
• Print pages 123 - 129 from the attached PDF file for your class
• #### During the Activity

Distribute the page to the class.

• Draw a circle with radius = 1/2 and find its perimeter
• Draw and measure the diameter of the circle
• Similarly draw four circles with radii r = 1, 2, 3, and 4
• Calculate the circumference/diameter ratio and check using the formula in the calculator
• Observe that the perimeter of the circle is given by 2πr, and the circumference divided by the diameter is always equal to π (3.1416)
• Set up a scatter plot with the circumference versus diameter data
• Guess the value of m in the equation for the line Y = mX
• Graph the predicted value and adjust the value until a line of best fit is obtained
• Note that Y = 3.1416X
• #### After the Activity

Review student results:

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