# Relationship between the circumference of a circle and its diameter.

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The formula for the circumference of a circle is pi*d, where pi is a constant (pi approximately 3.1415926) and d is the diameter of the circle.

Another formula for the circumference is C=2*pi*r where r is the radius of the circle. Note that the diameter is twice the length of the radius.

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The quotient of the circumference and the diameter of a circle is the constant pi.

pi=C/d

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Circumference of the circle = 2*pi*r ; where 'r' = radius of the circle

Now, radius of the circle 'r' = diameter of the circle/2

Thus, circumference of the circle = pi*d ; where 'd' = diameter of the circle