[tex]\bf \begin{cases}
\textit{area of a circle}=\pi r^2
\\ \quad \\
circumference=2\pi r
\end{cases}
\\ \quad \\
12.56=\pi r^2\implies \cfrac{12.56}{\pi }=r^2\implies \sqrt{\cfrac{12.56}{\pi }}=\boxed{r}
\\ \quad \\
thus
\\ \quad \\
circumference=2\pi \boxed{r}\implies 2\pi \boxed{\sqrt{\cfrac{12.56}{\pi }}}[/tex]
