LESSON 6.4
Solving Equations Involving Circumference and Perimeter
Goal: Solve equations involving the circumference of a circle.
Vocabulary
Circle:
Center:
Radius:
Diameter:
Circumference:
Pi ():
You can approximate π
22
using 3.14,
, or the π
7
key on a calculator
Circumference of a Circle
Words The circumference of a circle is the product of π and the ________________________ .
Algebra C = _________ or C = _________
EXAMPLE 1 - Using Radius to Find Circumference
Find the circumference of a circle with a radius of 15 feet.
EXAMPLE 2 - Using Diameter to Find Circumference
Find the circumference of the circle.
Now You Try It!
Find the circumference. Use 3.14 for π.
1)
2)
EXAMPLE 3
Standardized Test Practice
Basketball A basketball rim has a circumference of about 56.5 inches. What is its diameter? Use
3.14 for π.
A
9 inches
B
18 inches
C
24 inches
D
26 inches
.
Now You Try It!
Use 3.14 for π.
3) A circle has a circumference of 23.55 yards. Find the diameter.
4) A circle has a circumference of 352 miles. Find the radius.
Example 4 – Find the value of x if the perimeter of a rectangle is known.
Find the value of x if the perimeter is 26 feet. Then tell what the dimensions are (length and width).
x
x+3
Now You Try It!
5) Find the value of x if the perimeter is 46 feet. Then tell what the dimensions are (length and
width).
x
x+9
Example 5 – Problem solving with circumference.
Two circles are concentric if they share a center as in the diagrams below. The circumference of each
outer circle is given. Find x. Use 3.14 for .
C = 56.52 m