1. Area of Circles 10-5 Warm Up Problem of the Day Lesson Presentation
Course 1
Warm Up
Problem of the Day
Lesson Presentation

2. Area of Circles 10-5 Warm Up Evaluate. 1. 6  42 2. 5.6  23 96
Course 1
10-5
Area of Circles
Warm Up
Evaluate.
1. 6  42
 23
Simplify each expression.
n – 4
4. 5(n + 1) 96
44.8
n + 2
5n + 5

3. Area of Circles 10-5 Problem of the Day
Course 1
10-5
Area of Circles
Problem of the Day
What is the area of a right triangle with legs measuring 31 in. and 21 in.?
325.5 in2

4. Course 1
10-5
Area of Circles
Learn to find the area of a circle.

5. Course 1
10-5
Area of Circles
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6. Additional Example 1A: Estimating the Area of a Circle
Course 1
10-5
Area of Circles
Additional Example 1A: Estimating the Area of a Circle
Estimate the area of the circle. Use 3 to approximate pi.
Write the formula for area.
A = r2
19.7 m
Replace  with 3 and r with 20.
A ≈ 3 • 202
Use the order of operations.
A ≈ 3 • 400
A ≈ 1200 m2
Multiply.

7. Additional Example 1B: Estimating the Area of a Circle
Course 1
10-5
Area of Circles
Additional Example 1B: Estimating the Area of a Circle
Estimate the area of the circle. Use 3 to approximate pi.
A = r2
Write the formula for area.
r = d ÷ 2
The length of the radius is half the length of the diameter.
28 m
r = 28 ÷ 2
r = 14
Divide.
A ≈ 3 • 142
Replace  with 3 and r with 14.
A ≈ 3 • 196
Use the order of operations.
A ≈ 588 m2
Multiply.

8. Area of Circles 10-5 Check It Out: Example 1A
Course 1
10-5
Area of Circles
Check It Out: Example 1A
Estimate the area of the circle. Use 3 to approximate pi.
24.8 m
Write the formula for area.
A = r2
Replace  with 3 and r with 25.
A ≈ 3 • 252
Use the order of operations.
A ≈ 3 • 625
A ≈ 1875 m2
Multiply.

9. Area of Circles 10-5 Check It Out: Example 1B
Course 1
10-5
Area of Circles
Check It Out: Example 1B
Estimate the area of the circle. Use 3 to approximate pi.
A = r2
Write the formula for area.
r = d ÷ 2
The length of the radius is half the length of the diameter.
20 m
r = 20 ÷ 2
r = 10
Divide.
A ≈ 3 • 102
Replace  with 3 and r with 10.
A ≈ 3 • 100
Use the order of operations.
A ≈ 300 m2
Multiply.

10. Additional Example 2A: Using the Formula for the Area of a Circle
Course 1
10-5
Area of Circles
Additional Example 2A: Using the Formula for the Area of a Circle
Find the area of the circle. Use for pi. 22 7
8 ft
A = r2
Write the formula to find the area.
r = d ÷ 2
The length of the diameter is twice the length of the radius.
r = 8 ÷ 2 = 4
A  • (4)2 22 7
Replace  with and r with 4. 22 7 __
A  • 16  22 7 __
352 7
Use the order of operations.
A  ft2
Divide.

11. Additional Example 2B: Using the Formula for the Area of a Circle
Course 1
10-5
Area of Circles
Additional Example 2B: Using the Formula for the Area of a Circle
Find the area of the circle. Use for pi. 22 7
A = r2
Write the formula to find the area.
A  • 72 22 7
Replace  with and r with 7. 22 7 __
A  • 49 22 7 __ 7
Use the GCF to simplify. 1
A  154 cm2
Multiply.

12. Area of Circles 10-5 Check It Out: Example 2A
Course 1
10-5
Area of Circles
Check It Out: Example 2A
Find the area of the circle. Use for pi. 22 7
28 cm
A = r2
Write the formula to find the area.
r = d ÷ 2
The length of the diameter is twice the length of the radius.
r = 28 ÷ 2 = 14
A  • 142 22 7
Replace  with and r with 14. 22 7 __
A  • 196 22 7 __ 28
Use the GCF to simplify. 1
A  616 cm2
Multiply.

13. Area of Circles 10-5 Check It Out: Example 2B
Course 1
10-5
Area of Circles
Check It Out: Example 2B
Find the area of the circle. Use for pi. 22 7
7 cm
A = r2
Write the formula to find the area.
A  • 72 22 7
Replace  with and r with 7. 22 7 __
A  • 49 22 7 __ 7
Use the GCF to simplify. 1
A  154 cm2
Multiply.

14. Additional Example 3: Application
Course 1
10-5
Area of Circles
Additional Example 3: Application
A drum head has a radius of 18 in. Find the area of the material covering the drum head. use 3.14 for pi.
A = r2
Write the formula for area.
18 in.
A  3.14 • 182
Replace  with 3.14 and r with 18.
A  3.14 • 324
Use the order of operations.
A  1, in.2
Multiply.

15. Additional Example 3 Continued
Course 1
10-5
Area of Circles
Additional Example 3 Continued
A drum head has a radius of 18 in. Find the area of the material covering the drum head. use 3.14 for pi.
Check
18 in.
Use 3 as an estimate for. The area, r2, is approximately
3 • 182 = 3 • 324 = 972, so the answer is reasonable.

16. Area of Circles 10-5 Check It Out: Example 3
Course 1
10-5
Area of Circles
Check It Out: Example 3
A cymbal has a diameter of 18 in. Find its area. Use 3.14 for pi.
A = r2
Write the formula for area.
r = d ÷ 2
The length of the radius is half the length of the diameter.
18 m
r = 18 ÷ 2
r = 9
Divide.
A  3.14 • 92
Replace  with 3.14 and r with 9.
A  3.14 • 81
Use the order of operations.
A  m2
Multiply.

17. Check It Out: Example 3 Continued
Course 1
10-5
Area of Circles
Check It Out: Example 3 Continued
A drum head has a radius of 18 in. Find its area. Use 3.14 for pi.
Check
18 m
Use 3 as an estimate for. The area, r2, is approximately
3 • 92 = 3 • 81 = 243, so the answer is reasonable.

18. Insert Lesson Title Here
Course 1
10-5
Area of Circles
Insert Lesson Title Here
Lesson Quiz: Part I
Estimate the area of each circle.
27 km2
1200 yd2
3 km
38 yd

19. Insert Lesson Title Here
Course 1
10-5
Area of Circles
Insert Lesson Title Here
Lesson Quiz: Part II
Find the area of each circle. Use for pi. 22 7
2.4 cm
0.7 m
1.54 m2
4.53 cm2
5. A coater has a diameter of 6 inches. Find the area of the largest cup the coaster can hold. Use 3.14 for pi.
28.26 in2