Edible geometry

Students will use food to demonstrate their understanding of the sectors and arc lengths in a circle.

A lesson plan for grades 9–12 Mathematics

By shari frederick

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Learning outcomes

• to measure the radius of a circle
• to measure the central angle of a circle
• to calculate the area of a sector
• to calculate the length of an arc

Teacher planning

Time required for lesson

20 minutes

Materials/resources

• Rulers
• Protractors
• Big cookies(at least 8 in. in diameter)
• Plastic knives
• Napkins

Pre-activities

Students will need to know how to find the area and circumference of a circle. They will need to know about central angles and their corresponding minor arcs.

Activities

1. Divide the class into groups with varying numbers in each group. The number of groups should correspond to the number of cookies prepared.
2. Students are to decide how to divide the cookie fairly among the members of their group. They are to write down the measure necessary for the central angle. They are to measure the radius of their cookie.
3. Using this information, they should then discuss how knowing this information will help them to find the area of their slice. They also want to discuss how to find the length of the arc of their slice. Students are to calculate the following:
   • area of cookie
   • circumference of cookie
   • area of slice
   • length of arc on slice

Assessment

Students are to hand in one write-up per group of their findings. This should include all measurements taken as well as the number of members in their group.

Supplemental information

Comments

This is a fun way to end a lesson in which you have just discussed how to find the area and circumference of a circle. Whenever possible, I use this as a “Fun Friday” activity.