Instructional Activity# Making a Polygon out of a Circle

Lesson 8. Unit 3. Grade 7 Open Up Resources

Open Up Resources20 min(s)

This Instructional Activity is a part of the Lesson 8, Unit 3, Grade 7. In this activity, students cut and rearrange parts of a circle to approximate a parallelogram. They see that the area of the parallelogram would be calculated by multiplying half of the circle's circumference times its radius. Since students are not familiar with the process of writing proofs, it is necessary to walk them through writing the justification that uses the formula for the area of the parallelogram to develop the formula for the area of the circle. The construction in this activity shows that the constructed parallelogram has a height at most the radius of the circle and a base at most half the circumference of the circle.