Answer :

[tex]The\ area\ of\ the\ circle:A_O=\pi r^2\\\\The\ circumference\ of\ the\ circle:C_O=2\pi r\\===========================\\\\A_O=64\pi\Rightarrow\pi r^2=64\pi\\\\r^2=64\Rightarrow r=\sqrt{64}\Rightarrow r=6\\\\C_O=2\pi\cdot8=\boxed{16\pi}[/tex]
the circumference of a circle is [tex] \pi x^{2} [/tex]

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