An illustration of a circle showing the circumference, centre, diameter and radius.

are completely round shapes where every point from the center of the circle to its circumference is the same distance.

Relationship with piEdit

Pi can be used to calculate the circumference of a circle, which is similar to the perimeter of other shapes. The circumference of a circle is always exactly pi (3.1415...) times the diameter of the circle, no matter how large or the small the circle is. For example, a circle with diameter 10 would have an area of 31.415...

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