NAME
DATE
11-3
PERIOD
Study Guide and Intervention
Areas of Circles and Sectors
Areas Of Circles
If a circle has an area of A square units
and a radius of r units, then A = πr2.
Area of a Circle
Example
The area of a circle is equal to π times the square of radius.
Find the area of the circle p.
A = πr
2
O
r
Geo-SG11-03-08-860188
Area of a circle
= π(6)2
r=6
≈ 113.1
Use a calculator.
12 m
p
The area of the circle is about 113.1 square meters.
If d = 12 m, then r = 6 m.
C11-011A-890520-A
Exercises
Find the area of each circle. Round to the nearest tenth.
2.
9.5
78.5 in2
314.2 m2
4.C11-011A-890520-B
5.C11-011A-890520-C
283.5 in.
6.C11-011A-890520-D
11 in.
11 ft
95.0 ft2
6082.1 m2
C11-011A-890520-E
C11-011A-890520-F
Find
the indicated measure. Round
to the nearest tenth.
380.1 in2
C11-011A-890520-G
7. The area of a circle is 153.9 square centimeters. Find the diameter. 14.0 cm
8. Find the diameter of a circle with an area of 490.9 square millimeters. 25.0 mm
9. The area of a circle is 907.9 square inches. Find the radius. 17.0 in.
10. Find the radius of a circle with an area of 63.6 square feet. 4.5 ft
Chapter 11
19
Glencoe Geometry
Lesson 11-3
20 m
in.
5 in.
3.
88
m
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
1.
NAME
DATE
11-3
PERIOD
Study Guide and Intervention (continued)
Areas of Circles and Sectors
Areas of Sectors
intercepted arc.
A sector of a circle is a region bounded by a central angle and its
If a sector of a circle has an area of A square units,
a central angle measuring x°, and a radius of r units,
x
then A = −
πr2.
Area of a Sector
360
Example
Find the area of the shaded sector.
x
πr2
A=−
360
36
=−
π(5)2
360
≈ 7.85
Area of a sector
36° 5 in.
x = 36 and r = 5
Use a calculator.
The area of the sector is about 7.85 square inches.
Exercises
C11-012A-890520-A
Find the area of each shaded sector. Round to the nearest tenth.
2.
1.
3
ft
3.
L
100°
10
D F
20°
m
7m
K
45°
E
A
C
87.3 m2
C11-012A-890520-C
B
A
C
6.C11-012A-890520-D
D
5.
15°
K
88°
36°
10 m
F
L
J
52.4 ft
2
C11-012A-890520-E
E
cm
4.C11-012A-890520-B
20 ft
145.4 m2
7.
5
3.5 ft2
282.7 m2
C11-012A-890520-F
7. SANDWICHES For a party, Samantha wants to
have finger sandwiches. She cuts sandwiches into
circles. If she cuts each circle into three congruent
pieces, what is the area of each piece?
43.2 cm2
C11-012A-890520-G
2.5 in.
6.5 in2
Chapter 11
20
Glencoe Geometry
C11-012A-890520-H
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
B
J