[tex]\bf \textit{circumference of a circle}\\\\
C=2\pi r\qquad\qquad C=4\pi^2\implies 4\pi^2=2\pi r\implies \cfrac{4\pi^2}{2\pi }=r
\\\\\\
\boxed{2\pi =r}\\\\
-----------------------------\\\\
\textit{area of a circle}\\\\
A=\pi r^2\qquad \qquad A=\pi \left( \boxed{2\pi } \right)^2\implies A=\pi \cdot 4\pi^2\implies \boxed{A=4\pi^3}[/tex]
