Respuesta :

[tex]\bf \textit{area of a circle}\\\\ A=\pi r^2~~ \begin{cases} r=radius\\[-0.5em] \hrulefill\\ A=81\pi \end{cases}\implies 81\pi =\pi r^2\implies \cfrac{81\pi }{\pi }=r^2\implies 81=r^2 \\\\\\ \sqrt{81}=r\implies \boxed{9=r}~\hspace{10em}\stackrel{\textit{diameter = twice the radius}}{18}[/tex]

r3t40

[tex]

A=81\pi \\

A=\pi r^2 \\

81\pi=\pi r^2\Longrightarrow r^2=81

radius=\sqrt{81}=\boxed{9} \\

diameter=2radius = 2\cdot9=\boxed{18}

[/tex]

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