Building Blocks - Circles

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A circle is a closed curve in a plane. All of its points are an equal distance from its center. That distance is called the radius of the circle. A diameter is a line segment that has both of its endpoints on the circle and passes through the center.

A chord is a line segment with both endpoints on the circle. A portion of a circle is called an arc. A semicircle is an arc that is one-half of a circle.