Diameter d = 2 × r
Diameter d = C / p
Diameter d = square root (4 A / pi)
Circumference C = 2 p x r = p × d = square root (4 pi × A)
Area A = pi × (d × d / 4) = C2 / (4 × pi)
Radius r
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PI times the DIAMETER
diameter/2
diameter times 3.14159
The formula for the circumference of a circle is pi * diameter or (2 radius.)
two times the radius (d=2r)