Over Lesson 11–6
Find the area.
Find the area.
A.
B.
C.
D.
A
B
C
D
You have already found the perimeter of
rectangles. (Previous Course)
• Find the circumference of circles.
• Solve problems involving circumference.
• circle
•
The set of all points in a plane that are the same distance
from a given point called the center
given point from which all points on the circle are the
center The
same distance
• radius
• chord
The distance from the center to any point on the circle
A line segment whose endpoints are on a circle.
• diameter
A chord across through a circle’s center. Two radii are a
diameter
• circumference
•  (pi)
The distance around a circle
The ratio of the circumference of a circle to the diameter of
a circle. We typically say
Find the Circumference of a Circle
Find the circumference of the circle. Round to
the nearest tenth.
C = 2r
Circumference of a circle
= 2 ●  ● 7.1 Replace r with 7.1.
 44.6
Simplify. Use a calculator.
Answer: The circumference is about 44.6 meters.
Find the circumference of the circle
to the nearest tenth.
A. 5.0 cm
B. 8.0 cm
C. 10.1 cm
D. 32.2 cm
A.
B.
C.
D.
A
B
C
D
Find the Circumference of a Circle
Find the circumference of the circle. Round to
the nearest tenth.
C = 2r
Circumference of a circle
= 2 ●  ● 6 Replace r with 6 (Why?).
= 12
Simplify. This is the exact
circumference.
To estimate the circumference, use a calculator.
12
×
2nd
[]
ENTER
37.69911184
Answer: The circumference is about 37.7 inches.
Find the circumference of the circle to
the nearest tenth.
A. 12 ft
B. 12.6 ft
C. 25.1 ft
D. 50.3 ft
A.
B.
C.
D.
A
B
C
D
Solve Problems
LANDSCAPING A landscaper has a tree whose
roots form a ball-shaped bulb with a circumference
of 110 inches. What is the minimum diameter of the
hole that the landscaper will have to dig in order to
plant the tree? Round to the nearest inch.
Understand
You know the circumference of the roots
of the tree. You need to know the
diameter of the hole to be dug.
Plan
Use the formula for the circumference of
a circle to find the diameter.
Solve Problems
Solve
C = 2r
110 = 2 ●  ● r
Circumference of a
circle
Replace C with 110.
Divide each side by .
Simplify
35.0  d
2r is the diameter.
Answer: The diameter of the hole should be at least
35 inches.
Solve Problems
Check
Is the solution reasonable? Check by
replacing d with 35 in C = d.
C = d
Circumference of a circle
C =  ● 35
Replace d with 35.
C  110.0
Simplify. Use a
calculator.
The solution is reasonable.
SWIMMING POOL A circular swimming pool has a
circumference of 48 feet. Matt must swim across the
diameter of the pool. How far will Matt swim?
A. 7.6 ft
B. 15.3 ft
C. 47.1 ft
D. 150.7 ft
A.
B.
C.
D.
A
B
C
D