[tex]\bf \textit{circumference of a circle}\\\\
C=2\pi r~~
\begin{cases}
r=radius\\
-----\\
C=\frac{3\pi }{4}
\end{cases}\implies \cfrac{3\pi }{4}=2\pi r
\\\\\\
\cfrac{3\pi }{4(2\pi )}=r\implies
\boxed{\cfrac{3}{8}=r}\\\\
-------------------------------\\\\
\textit{area of a circle}\\\\
A=\pi r^2\qquad \qquad \implies A=\pi \left( \boxed{\frac{3}{8}} \right)^2\implies A=\pi \left( \cfrac{3^2}{8^2} \right)
\\\\\\
A=\cfrac{9\pi }{64}[/tex]
