The Circle
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The circle is a set of points equally distant from one central point. This central point is called the center of the circle. Here the center is shown with a small cross. The distance from the center to the curve of the circle is called the radius. Here the radius is shown as a line from the center to the curve of the circle.
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The distance across the circle is called the diameter. The diameter always passes through the center of the circle. The diameter is equal in length to twice the radius.
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The distance all the way around the circle is called the circumference. The circumference is usually symbolized with a 'C' as shown here. The length of the circumference is equal to 2 times pi times the radius.
Usually, as here, the radius is symbolized with an 'r'.
Common Shapes Geometry Mathematics Contents Index Home