7­7: Circumference of a Circle
Radius and Diameter
The radius is the distance from one side of the circle to the center of the circle. The radius is one­half the length of the diameter.
The diameter starts at one side of the circle, goes directly through the center and to the opposite side of the circle. The diameter is two times the length of the radius.
Circumference of a circle
Circumference is the distance around a circle. It is the perimeter of a circle.
Diameter
Drag and drop the word and label the circles correctly. diameter
radius
There are 2 formulas to solve for circumference. 1) 2 r or 2) d
r = radius
d = diameter
= Pi = 3.14
1
How to solve for circumference using the given formulas.
When given the diameter:
multiply 3.14 (Pi) x diameter to solve.
21.98
6
3)
1)
31.40
47.10
7
When given the radius:
multiply 3.14 (Pi) x 2 x radius to solve. 5
15
diameter
In this example, multiply 3.14 x 7 to solve the problem.
Move this box to reveal the answer.
Solve the following problems using the circumference formulas.
2)
2
12.56
4)
20
62.80
In this example, multiply 3.14 x 2 x 6 to solve the problem.
Click the blue rectangle to reveal the answer.
37.68
Move this box to reveal the answer.
After one complete turn of the wheel, it will have traveled
81.6 inches. What is the diameter of the bicycle wheel?
Homework:
Pages 299 and 300
#12­14,
20­ 26,
28­31
:
2