1. Objective: Find the circumference and area of circles
Mr. Peter Richard
Wears Cool Glasses Too!
Objective: Find the circumference and area of circles

2. Circle – Label the parts
Diameter
Radius

3. Circumference: C=2 r
Circumference is the length of the distance AROUND the circle
Take 2 times the radius and pi

4. Circumference: C=2∏r Find the circumference of a circle with radius 5.
Find the circumference of a circle with diameter 10.
5 in.
10 in.

5. Circumference Find the circumference of a circle with radius 2.
Find the circumference of a circle with diameter 8.

6. Area of a Circle
Area of a circle is the amount of space the circle covers.

7. Area of a Circle
Find the area of a circle with radius 9.
9 feet

8. Find the area of the circles below.1) 2)
6 in.
16 m

9. Area of a Circle
Find the area of a circle with radius 5.

10. Area of a Circle
Find the area of a circle with diameter 24.

11. Instructional Conversation
Problem #2
Find the circumference. 4

12. Instructional Conversation
Problem #4
Find the area. 20

13. Additional Example 3: Application
Find the area of the shaded region of the circle. Use 3.14 for  . Round your answer to the nearest tenth.
1.5 cm
The measurement of the radius of the circle is 1.5 cm.
Now find the area of the entire circle.
A = r2
Use the formula for the area of a circle.
A = 3.14 · 1.52
Substitute. Use 1.5 for r.
A  3.14 · 2.25
Evaluate the power.
A  7.07
Multiply.

14. Additional Example 3 Continued
Find the area of the shaded region of the circle. Use 3.14 for  . Round your answer to the nearest tenth.
Since of the circle is shaded, divide the area of the
circle by ÷ 2 =
1 2
The area of the shaded region of the circle is about 3.5 cm2.

15. Check It Out: Example 3
Find the area of the shaded region of the circle. Use 3.14 for  . Round your answer to the nearest tenth.
2.4 cm
The measurement of the radius of the circle is 2.4 cm.
Now find the area of the entire circle.
A = r2
Use the formula for the area of a circle.
A = 3.14 · 2.42
Substitute. Use 2.4 for r.
A  3.14 · 5.76
Evaluate the power.
A  18.09
Multiply.

16. Check It Out: Example 3 Continued
Find the area of the shaded region of the circle. Use 3.14 for  . Round your answer to the nearest tenth.
Since of the circle is shaded, divide the area of the
circle by 4 and subtract the answer from the entire area ÷ 4 = – 4.52 =
3 4
The area of the shaded region of the circle is about cm2.

17. Time To Circle Your Answers!
Quiz: Worksheet
Homework: Worksheet