1. Lesson 6.4 Solving Equations Involving Circumference
Essential Question: How do you find the circumference of a circle?

2. Before we start…
In a Chinese tea service set, one saucer has a diameter of 6.75 cm. A cup has a circumference of cm. Will the cup fit in the saucer?

3. What is a circle?
A circle is the set of all points in a plane that are the same distance from a fixed point called the center.

4. The radius is the distance from the center to any point on the circle.
The diameter is the distance across the circle through the center, or twice the radius.

5. What is the circumference?
The distance around the circle. Circumference is the name for the perimeter of a circle.
For every circle, the quotient of its circumference and its diameter is the same: about This is represented by the Greek letter pi, π.

6. How do I find the circumference of a circle?
The circumference of a circle is the product of π and the diameter.
𝐶=𝜋𝑑 or 𝐶=2𝜋𝑟
If you know the circumference of the circle, you could find it’s diameter and radius.

7. Find the circumference of a circle with a radius of 11 meters.

8. Find the circumference.

9. Find the circumference of the circle.

10. A Ferris wheel has a circumference of about 423. 9 feet
A Ferris wheel has a circumference of about feet. What is the diameter of the Ferris wheel? Use 3.14 for π.

11. A pottery wheel has a circumference of 44 inches. Find the radius
A pottery wheel has a circumference of 44 inches. Find the radius. Use 3.14 for π.

12. A circular swimming pool has a circumference of 62 feet 10 inches
A circular swimming pool has a circumference of 62 feet 10 inches. What is the diameter of the pool in feet? Use 3.14 for π. Round to the nearest hundredth.

13. The radius of the top of an eraser on a pencil is 3. 5 mm
The radius of the top of an eraser on a pencil is 3.5 mm. Find the circumference of the eraser.

14. A basketball hoop has a circumference of about 56. 5 inches
A basketball hoop has a circumference of about 56.5 inches. A basketball has a circumference of about 28.5 inches. What is the approximate difference between the diameter of the hoop and the diameter of the basketball?

15. Find the perimeter of the figure. Use 3.14 for π.

16. Find the perimeter of the figure. Use 3.14 for π.

17. How do you find the circumference of a circle?

18. Ticket Out the Door
The diameter of the U.S. Capitol Building’s dome is 96 feet at its widest point. Find its circumference. Use 3.14 for π.