Diameter
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The circumference of a circle is equal to its diameter times pi. This is also equal to two times its radius times pi.
2R or two times the radius.
The circumference of a circle is 2*pi*radius or pi*diameter
two times the radius times pi
The formula for a circle's area is pi*radius*radius.The diameter is equal to two times the radius.D = 2*radiusSo, the radius is 4.5 cmArea = pi*radius*radius = 3.14159 * 4.5cm * 4.5cm = 63.617 cm2