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(7) Lesson 8.2
1. Find the radius or diameter of each circle with the given
dimensions.
1. d = 6 cm
2. r = 11 ft
Find the circumference of each circle. Use 3.14 for Ο. Round to
the nearest tenth if necessary.
3. 4.
5. Charlotte has a trampoline in her backyard. The diameter of the
trampoline is 14 feet. What method can Charlotte use to find the
circumference of the trampoline?
Course 2, Lesson 8-2
2. Course 2, Lesson 8-2
ANSWERS
1. r = 3 cm
2. d = 22 ft
3. 31.4 cm
4. 40.8 in.
5. Multiply the diameter by Ο.
7. Course 2, Lesson 8-2
Geometry
Words The area A of a circle equals Model
the product of and the square
of its radius r.
Symbols A =
ο°
2
rο°
8. 1
Need Another Example?
2
3
4
Step-by-Step Example
1. Find the area of the circle.
Use 3.14 for Ο.
Area of a circleA = Οr2
Check for Reasonableness
The area of the circle is approximately 12.56 square inches.
Estimate 3 Γ 2 Γ 2 = 12
A β 3.14 β’ 22
A β 3.14 β’ 4
A β 12.56
Replace r with 2.
22 = 2 β’ 2 = 4
Multiply.
12.56 β 12
10. 1
Need Another Example?
2
3
4
Step-by-Step Example
2. Find the area of a circle with a radius of 14 centimeters.
Use for Ο.
Area of a circleA = Οr2
Check for Reasonableness
The area of the circle is approximately
616 square centimeters.
Estimate
28
1
616 β 588
3 Γ 14 Γ 14 = 588
A β β’ 142
A β β’ 196
A β β’ 196
A β 616
Replace Ο with and r with 14.
142 = 14 β’ 14 = 196
Divide by the GCF, 7.
Multiply.
12. 1
Need Another Example?
2
3
4
5
Step-by-Step Example
3. Find the area of the face of the Virginia quarter with
a diameter of 24 millimeters. Use 3.14 for Ο. Round
to the nearest tenth if necessary.
The area is approximately 452.2 square millimeters.
The radius is (24) or 12 millimeters.
A = Οr2 Area of a circle
A β 3.14 β’ 122 Replace r with 12.
A β 452.16 Multiply.
13. Answer
Need Another Example?
Find the area covered by the fountain. Use 3.14 for Ο.
Round to the nearest tenth if necessary.
21.2 m2
14. Need Another Example?
Step-by-Step Example
4. Find the area of the semicircle.
Use 3.14 for Ο. Round to the
nearest tenth.
1
2
3
4
5
A = Οr2 Area of a semicircle
A β (3.14)82 Replace r with 8.
A β 0.5(3.14)(82) 82 = 8 β’ 8 or 64
A β 100.5 Simplify.
The area of the semicircle is approximately 100.5 square inches.
16. 1
Need Another Example?
2
3
4
5
Step-by-Step Example
5. On a basketball court, there is a semicircle above the
free-throw line that has a radius of 6 feet. Find the area of
the semicircle. Use 3.14 for Ο. Round to the nearest tenth.
So, the area of the semicircle is approximately 56.5 square feet.
A = Οr2 Area of a semicircle
A β 0.5(3.14)(62) Replace Ο with 3.14 and r with 6.
A β 0.5(3.14)(36) 62 = 6 β’ 6 = 36
A β 56.5 Multiply.
17. Answer
Need Another Example?
Tarie is cutting material in the shape of semicircles for
her craft project. What is the area of the semicircle? Use
3.14 for Ο. Round to the nearest tenth if necessary.
100.5 in.2
18. How did what you learned
today help you answer the
Course 2, Lesson 8-2
Geometry
HOW do measurements help you
describe real-world objects?
19. How did what you learned
today help you answer the
Course 2, Lesson 8-2
Geometry
HOW do measurements help you
describe real-world objects?
Sample answers:
β’ To find the area of a circular object, such as the area of
a radio signal
β’ To find the area of a semicircular object, such as
window
20. Suppose you have a circular
rug in your living room. Describe
how you would find the area
of the rug and which measures
you would need to know
in order to find its area.
Course 2, Lesson 8-2
Ratios and Proportional RelationshipsFunctionsGeometry