In these lessons, we will learn
A circle is a closed curve formed by a set of points on a plane that are the same distance from its center. The circumference of a circle is the distance around the circle. It is sometimes called the perimeter of a circle.
Calculating the circumference of a circle involves a constant called pi with the symbol π. Pi (π) is the ratio of the circumference of a circle to its diameter. Pi is always the same number for any circle.
The value of π (pi) is approximately 3.14159265358979323846... but usually rounding to 3.142 should be sufficient. (see a mnemonic for π)
The formula for the circumference of a circle is
C = πd (see a mnemonic for this formula)
C = 2πr
where C is the circumference, d is the diameter and r is the radius.
The diameter of a circle is a line segment that passes through the center of the circle and has its endpoints on the circle. The radius of the circle is a line segment from the center of the circle to a point on the circle. The diameter of a circle is twice the length of its radius.
If you are given the diameter then use the formula C = πd
If you are given the radius then use the formula C = 2πr
The formula for the circumference of a circle is the product of pi (π) and the diameter or twice the product of pi (π) and the radius.
Find the circumference of the circle with a diameter of 8 inches.
|Step 1: Write down the formula:||C = πd|
|Step 2: Plug in the value:||C = 8π|
Answer: The circumference of the circle is 8π ≈ 25.163 inches.
Find the circumference of the circle with a radius of 5 inches.
|Step 1: Write down the formula:||C = 2πr|
|Step 2: Plug in the value:||C = 10π|
Answer: The circumference of the circle is 10 π ≈ 31.42 inches.
|Worksheet to calculate circumference of circle when given diameter or radius.||Worksheet to calculate circumference and area of circle when given diameter or radius.|
From the formula C = 2πr, we see that we can find the radius of a circle by dividing its circumference by 2π.The following video shows how to find the radius of a circle given its circumference.
From the formula C = πd, we see that we can find the diameter of a circle by dividing its circumference by π.Example: A circle has a circumference of 12 cm. Find the radius.
To find the area of a circle when given the circumference, we first use the circumference to find the radius. Then, we use the radius to find the area of the circle.
|Worksheet Calculate problems that involve the radius, diameter, circumference and area of circle.||Worksheet 1Word problems that involve circles.|
|Worksheet 2 Word problems that involve circles.|
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