1. 11-3 Areas of Circles and Sectors
You found the circumference of a circle.
Find areas of circles.
Find areas of sectors of circles.

2. A = π·r2 Area of a Circle A = area r = radius
The formula for area of a circle is:
A = π·r2
A = area r = radius
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3. If the radius of סּC is 3 cm, what is its area? Answer in exact form.

4. MANUFACTURING An outdoor accessories company manufactures circular covers for outdoor umbrellas. If the cover is 8 inches longer than the umbrella on each side, find the area of the cover in square inches.
The diameter of the umbrella is 72 inches, and the cover must extend 8 inches in each direction. So, the diameter of the cover is or 88 inches. Divide by 2 to find that the radius is 44 inches.
Area of a circle
Substitution
Use a calculator.
Answer: The area of the cover is about 6082 square inches.

5. A swimming pool company manufactures circular covers for above ground pools. If the cover is 1 foot longer than the pool on each side, find the area of the cover.
A ft2
B ft2
C ft2
D ft2

6. If the area of סּC is 49π, what is its diameter?
π π
49 = r2
r = 7

7. ALGEBRA Find the radius of a circle with an area of 58 square inches.
Area of a circle
Substitution
Divide each side by .
Take the positive square root of each side.
= r
Simplify.
4.3 ≈ r
Answer: The radius of the circle is about 4.3 in.

8. ALGEBRA Find the radius of a circle with an area of 45 square inches.
A. 3.8 in.
B. 4.5 in.
C. 5.7 in.
D. 7.6 in.

9. The South Rose window in Notre Dame has a diameter of 12. 9 meters
The South Rose window in Notre Dame has a diameter of 12.9 meters. Find the area and circumference of the window.
C = 2πr
C = 2π(12.9)
C = 25.8π
C = meters
A = π·r2
A = π(12.9)2
A = π
A = meters2

10. If the area of סּM is 121 m2, find its circumference.
π π
38.5 = r2
r = 6.2 m
C = 2πr
C = 2π(6.2)
C = m סּM
What letter is common to both the area and circumference formulas?
r (radius)

11. Sector Area
Sector area is the wedge-shaped interior regions of a circle formed by central angles.

12. A sector of a circle is a region formed by two radii and an arc of circle. ABC is a sector of סּB

13. Formula for Sector Length
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14. is a central angle of סּK
Find the area of sector JKL to the nearest tenth. J K L
125°
12 cm
The arc covers 125° out of a total of 360° or

15. PIE A pie has a diameter of 9 inches and is cut into 10 congruent slices. What is the area of one slice to the nearest hundredth?
Step 1 Find the arc measure of a pie slice.
Since the pie is equally divided into slices, each slice will have an arc measure of 360 ÷ 10 or 36.
Step 2 Find the radius of the pie. Use this measure to find the area of the sector, or slice.
The diameter is 9 inches, so the radius is 4.5 inches.
Area of a sector
x = 36 and r = 4.5
Use a calculator.
Answer: The area of one slice of pie is about 6.36 square in.

16. PIZZA A pizza has a diameter of 14 inches and is cut into 8 congruent slices. What is the area of one slice to the nearest hundredth?
A in2
B in2
C in2
D in2

17. 11-3 Assignment
Page 801, 8-22 even