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Table of Content
Table of Content
What is a 'radius'.
What is a 'radius'.
The radius of a circle is the line drawn from the center of a circle to the circumference.
What is a 'diameter'.
What is a 'diameter'.
The diameter of a circle is the line that cuts a circle in half and passes through the center of a circle
Facts: the diameter is twice as long as the radius.
What is a 'Circumference'?
What is a 'Circumference'?
The term 'circumference' is typically used in reference to circles.
The circumference of a circle is the perimeter of the circle.
It is the total length of the boundary of the circle.
How is 'Circumference' calculated?
How is 'Circumference' calculated?
The circumference ( c ) of a circle is the product of ...
a constant called pie, π, and the diameter (d) of the circle.
c = π d
In short: whatever the diameter is, you multiply it by π
Example 1
Example 1
Find the circumference of a circle with a diameter of 9cm.
c = πd
c = π*(9) = 9π
c = 28.2 cm
Example 2
Example 2
Find the circumference of a circle with a diameter of 30cm.
c = πd
c = π*(9) = 9π cm
c = 94.2 cm
Fact 2:
For any circle, it take a little more that 3 diameters (3.14 to be exact) to go around the circumference of a circle.
What is π
What is π
Fact:
The ratio of the circumference of any circle to its diameter is equal to a constant number called pie (π).
For any circle, it take a little more that 3 diameters (3.14 to be exact) to go around the circumference of a circle.
Diameter vs Radius
Diameter vs Radius
The diameter of any circle is...
twice its radius
So, if the...
radius is 5, the diameter 2(5) =10
radius is 11, the diameter 2(11) =22
Finding Circumference in terms of Radius
Finding Circumference in terms of Radius
Recall that Circumference (c) of a circle was given as...
c = π d
Since d = 2r, we can write...
c = π(2r)
c= 2πr
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