[tex]\bf \textit{arc's length}\\\\
s=r\theta ~~
\begin{cases}
r=radius\\
\theta =angle~in\\
\qquad radians\\
------\\
r=6\\
s =\frac{3\pi }{4}
\end{cases}\implies \cfrac{3\pi }{4}=6\theta \implies \cfrac{3\pi }{24}=\theta
\\\\\\
\stackrel{simplified}{\cfrac{\pi }{8}=\theta }[/tex]
