[tex]\bf \textit{circumference of a circle}\\\\
C=2\pi r\quad
\begin{cases}
r=radius\\
-----\\
C=2
\end{cases}\implies 2=2\pi r\implies \cfrac{2}{2\pi }=r\implies \cfrac{1}{\pi }=r
\\\\\\
\textit{its area will then be }A=\pi r^2\implies A=\pi \left( \frac{1}{\pi } \right)^2\implies A=\cfrac{1}{\pi } \\\\
-------------------------------[/tex]
[tex]\bf \textit{circumference of a circle}\\\\
C=2\pi r\quad
\begin{cases}
r=radius\\
-----\\
C=4
\end{cases}\implies 4=2\pi r\implies \cfrac{2}{\pi }=r
\\\\\\
\textit{its area will then be }A=\pi r^2\implies A=\pi \left( \frac{2}{\pi } \right)^2\implies A=\cfrac{4}{\pi }[/tex]
