1. Five-Minute Check (over Lesson 11–2) Then/Now New Vocabulary
Key Concept: Area of a Circle
Example 1: Real-World Example: Area of a Circle
Example 2: Use the Area of a Circle to Find a Missing Measure
Key Concept: Area of a Sector
Example 3: Real-World Example: Area of a Sector
Lesson Menu

2. Find the area of the figure. Round to the nearest tenth if necessary.
A. 202 units2
B. 198 units2
C units2
D units2
5-Minute Check 1

3. Find the area of the figure. Round to the nearest tenth if necessary.
A. 96 units2
B units2
C units2
D units2
5-Minute Check 2

4. Find the area of the figure. Round to the nearest tenth if necessary.
A. 70 units2
B units2
C. 75 units2
D units2
5-Minute Check 3

5. Find the area of the figure. Round to the nearest tenth if necessary.
A units2
B. 117 units2
C. 198 units2
D. 234 units2
5-Minute Check 4

6. Trapezoid LMNO has an area of 55 square units. Find the height.
A. 6 units
B. 5 units
C. 4 units
D. 3 units
5-Minute Check 5

7. The area of a kite is 120 square meters
The area of a kite is 120 square meters. The length of one diagonal is 15 meters. Find the length of the other diagonal.
A. 4 m
B. 8 m
C. 16 m
D m
5-Minute Check 6

8. Splash Screen

9. 11-3 Areas of Circles and Sectors (Pg.782)
TARGETS
Find areas of circles.
Find areas of sectors of circles.
Then/Now

10. Content Standards   
G-C.5 Find arc lengths and areas of sectors of circles.
G-GMD.1 Explain volume formulas and use them to solve problems.
Mathematical Practices
4 Model with mathematics.
1 Make sense of problems and persevere in solving them.
Then/Now

11. You found the circumference of a circle. (Lesson 10–1)
Find areas of circles.
Find areas of sectors of circles.
Then/Now

12. sector of a circle
segment of a circle
Vocabulary

13. Concept 1

14. Area of a Circle
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.
Example 1

15. Answer: The area of the cover is about 6082 square inches.
Area of a Circle
Area of a circle
Substitution
Use a calculator.
Answer: The area of the cover is about 6082 square inches.
Example 1

16. 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
Example 1

17. ALGEBRA Find the radius of a circle with an area of 58 square inches.
Use the Area of a Circle to Find a Missing Measure
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.
Example 2

18. 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.
Example 2

19. Concept 2

20. Step 1 Find the arc measure of a pie slice.
Area of a Sector
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.
Example 3

21. Answer: The area of one slice of pie is about 6.36 square inches.
Area of a Sector
Area of a sector
x = 36 and r = 4.5
Use a calculator.
Answer: The area of one slice of pie is about square inches.
Example 3

22. 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
Example 3

23. End of the Lesson