Question

The circumference of a circle is 60π cm. What is the length of an arc of 140°?

Answer 1

`\bf \textit{circumference of a circle}\\\\ C=2\pi r~~ \begin{cases} r=radius\\ \cline{1-1} C=60\pi \end{cases}\implies 60\pi =2\pi r\implies \cfrac{\stackrel{30}{~~\begin{matrix} 60\pi \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~} }{~~\begin{matrix} 2\pi\\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~ }=r\implies 30=r \\\\[-0.35em] ~\dotfill`

`\bf \textit{arc's length}\\\\ s=\cfrac{\pi \theta r}{180}~~ \begin{cases} r=radius\\ \theta =angle~in\\ \qquad degrees\\ \cline{1-1} r=30\\ \theta =140 \end{cases}\implies s=\cfrac{\pi (140)(30)}{180}\implies s=\cfrac{70\pi }{3} \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ ~\hfill s\approx 73.30~\hfill`