Education Technology

Constructing the Diameter of a Circle

Activity Overview

Given a circle, students will construct a diameter of the circle.
They will use the following theorem: In the same circle, if one chord is a perpendicular bisector of another chord, then the first chord is a diameter.

Before the Activity

Students should have access to either the TI-83 or TI-84 family of calculators and a copy of the attached document.

During the Activity

All directions are in the attached document. A sample final product is in the attached application variable.
1. Open the Cabri Jr. App. and clear the screen. 2. Draw a circle. 3. Draw segment AB as a chord of the circle. 4. (Optional) Label points A and B. 5. Construct the perpendicular bisector of segment AB. 6. Create segment CD, which is the intersection of the perpendicular bisector of segment AB with the circle. 7. Label points C and D. 8. Hide the perpendicular bisector of segment AB (but not segment AB), segment CD, A and B. 9. Grab the radius point and move it around the screen to see that segment CD remains a diameter of the circle no matter how large or small the circle. 10. (Optional) Save the application variable.

After the Activity

Review student answers:

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