[tex]In~primul~rand~trebuie~sa~stii~formula~pentru~luncgimea~cercului. \\ \\ \boxed{L=2 \pi R} \\ \\ Pentru~aflarea~lungimii~unui~arc~de~cerc,~folosim~regula~de~trei \\ \\ simpla. \\ \\ 360 \textdegree................................2 \pi R \\ u \textdegree ...................................x \\ -------------- \\ x= \frac{2 \pi R \cdot u \textdegree} {360 \textdegree} = \frac{ \pi R \cdot u \textdegree}{180 \textdegree} .[/tex]
[tex]Deci~formula~este: \\ \\ \boxed{L_{arc}= \frac{ \pi R \cdot u \textdegree}{180 \textdegree} }~unde~u~este~masura~unghiului~la~centru~determinat~ \\ \\ de~extremitatile.[/tex]
