[tex]\bf \textit{circumference of a semi-circle}\\\\
C=\pi r\qquad
\begin{cases}
r=radius\\
-----\\
C=5.14
\end{cases}\implies 5.14=\pi r\implies \boxed{\cfrac{5.14}{\pi }=r}\\\\
-------------------------------\\\\
\textit{area of a semi-circle}\\\\
A=\cfrac{\pi r^2}{2} \implies A=\cfrac{\pi }{2}r^2\implies A=\cfrac{\pi }{2}\left( \boxed{\cfrac{5.14}{\pi }} \right)^2
\\\\\\
A=\cfrac{\pi }{2}\implies \cfrac{5.14^2}{\pi ^2}\implies A=\cfrac{26.4196}{2\pi }\implies A=\cfrac{13.2098}{\pi }[/tex]
