Respuesta :

[tex]\bf \textit{arc's length}\\\\ s=\cfrac{\pi \theta r}{180}~~ \begin{cases} r=radius\\ \theta =angle~in\\ \qquad degrees\\[-0.5em] \hrulefill\\ r=1\\ \theta =72 \end{cases}\implies s=\cfrac{\pi (72)(1)}{180}\implies s=\cfrac{2\pi }{5}[/tex]