1. • Area of Circles AREA OF A CIRCLE A = r2
Course 2
Area of Circles
AREA OF A CIRCLE
The area A of a circle is the product of  and the square of the circle’s radius r.
A = r2 • r

2. Area of Circles Example 1
Course 2
Area of Circles
Example 1
Find the area of the circle to the nearest tenth. Use 3.14 for .
A = r2
Use the formula.
7 cm
A  3.14 · 72
Substitute 7 for r.
A  3.14 · 49
Evaluate the power.
A 
Multiply.
The area of the circle is about cm2.
The order of operations calls for evaluating the exponents before multiplying.
Remember!

3. Area of Circles Example 2
Course 2
Area of Circles
Example 2
Find the area of the circle to the nearest tenth. Use 3.14 for .
A = r2
Use the formula.
18 ft
A  3.14 · 92
Substitute 9 for r.
A  3.14 · 81
Evaluate the power.
A 
Multiply.
The area of the circle is about ft2.

4. Find the area of the circle to the nearest tenth. Use 3.14 for .
Example 3
Find the area of the circle to the nearest tenth. Use 3.14 for .
A = r2
Use the formula.
10 cm
A  3.14 · 102
Substitute 10 for r.
A  3.14 · 100
Evaluate the power.
A  314
Multiply.
The area of the circle is about 314 cm2.
Course 2

5. Area of Circles Example 4
Course 2
Area of Circles
Example 4
Find the area of the circle to the nearest tenth. Use 3.14 for .
A = r2
Use the formula.
12 ft
A  3.14 · 62
Substitute 6 for r.
A  3.14 · 36
Evaluate the power.
A 
Multiply.
The area of the circle is about ft2.

6. Area of Circles Example 5
Course 2
Area of Circles
Example 5
Albert was designing a cover for a spa. If the radius of the spa is 7 ft, what is the area of the cover that will be made? Use 22 7
for .
A =  r2
Use the formula for the area of a circle. 22 7
A 
·72
Substitute. Use 7 for r. 7 22 7
A  49
Evaluate the power. 1
A  22 · 7
A  154
Multiply.
The area of the top that will cover spa is about 154 ft2.

7. Area of Circles Example 6: Application
Course 2
Area of Circles
Example 6: 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.

8. Example 6 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.

9. Area of Circles Example 7
Course 2
Area of Circles
Example 7
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.

10. Area of Circles Example 7 Continued
Course 2
Area of Circles
Example 7 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.

11. Insert Lesson Title Here
Course 2
Area of Circles
Insert Lesson Title Here
Lesson Quiz
Find the area of each circle, to the nearest tenth. Use 3.14 for . 1.
3. The bull’s-eye on a target has a diameter of 2 in. What is the area of the bull’s-eye to the nearest tenth? Use 3.14 for .
4. A round table cloth has a radius of 36 in. What is the area of the table cloth? Use 3.14 for . Round your answer to the nearest tenth. 2.
9 ft
8 ft • •
201.0 ft2
63.6 ft2
3.1 in2
4,069.4 in2