2. Main Idea and New Vocabulary Key Concept: Circumference of a Circle
Example 1: Find the Circumferences of Circles
Example 2: Find the Circumferences of Circles
Key Concept: Area of a Circle
Example 3: Find the Areas of Circles
Example 4: Real-World Example
Lesson Menu

3. Find the circumference and area of circles.
center
radius
chord
diameter
circumference pi
Main Idea/Vocabulary

4. Key Concept

5. Find the Circumferences of Circles
Find the circumference of the circle. Round to the nearest tenth.
C = d Circumference of a circle
C =  • 5 Replace d with 5.
C = 5 This is the exact circumference.
Use a calculator to find 5 []
ENTER ×
2nd
Answer: The circumference is about 15.7 feet.
Example 1

6. Find the circumference of the circle. Round to the nearest tenth.
A cm
B cm
C cm
D cm
Example 1 CYP

7. Find the Circumferences of Circles
Find the circumference of the circle. Round to the nearest tenth.
C = 2r Circumference of a circle
C = 2 •  • 3.8 Replace r with 3.8.
C ≈ Use a calculator.
Answer: The circumference is about 23.9 meters.
Example 2

8. Find the circumference of the circle. Round to the nearest tenth.
A mm
B mm
C mm
D mm
Example 2 CYP

9. Key Concept 4

10. Find the Areas of Circles
Find the area of the circle. Round to the nearest tenth.
A = r2 Area of a circle
A = (5)2 Replace r with half of 10 or 5.
A =  • 25 Evaluate 52. This is the exact area.
A ≈ Use a calculator.
Answer: The area is about 78.5 square inches.
Example 3

11. Find the area of the circle. Round to the nearest tenth.
A yd2
B yd2
C yd2
D yd2
Example 3 CYP

12. C = d Circumference of a circle 84 = d Replace C with 84.
TREES The circumference of a tree is 84 inches. What is the approximate diameter of the tree?
C = d Circumference of a circle
84 = d Replace C with 84.
Divide each side by .
26.7 ≈ d Use a calculator.
Answer: The diameter of the tree is about 27 inches.
Example 4

13. BICYCLES The circumference of a bicycle wheel is 53. 4 inches
BICYCLES The circumference of a bicycle wheel is 53.4 inches. What is the approximate diameter of the wheel?
A. 9 in.
B. 15 in.
C. 17 in.
D. 20 in.
Example 4 CYP