pi x diameter
diameter=radius2
9x2=18
18xpi=56.548
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2 inch radius = 12 9/16" circumference & an area of 12.56637 sq. inches.
r2*pie=circumference 9(9)*pie 81*pie 254
C = 2*pi*r Plug in.
Circumference of 9 inches: 2.864788975654119in. (for pi I used 3.14159265358979) Diameter of 9 inches: 4.5in.
If a circle has a circumference of 18pi, the radius is 9.