Figure 1. |
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Above, we have a circle.

Figure 2. |
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The distance from one side of the circle to the center is called the radius.

Figure 3. |
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The distance from one side of the circle to another, while going through the center, is called the diameter.

Figure 4. |
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The distance all the way around a circle is called the circumference.

Figure 5. |
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Here we have a circle with a radius of 4. We can use that information to find the circle's area:

Circumference of a Circle |
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So, for our circle:

Circumference = 2(3.14)(4)

Circumference = 25.12