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[tex]l = R \times \alpha [/tex]
[tex]l = length \: \: of \: \: the \: \: arc[/tex]
[tex]R = radius = 13 \: \: km[/tex]
[tex] \alpha = mersure \: \: of \: \: the \: \: centeral \: \: angle \: \: between \: \: two \: \: radiuses \\ [/tex]
Hint :
[tex] \alpha \: \: must \: \: be \: \: in \: \: radian[/tex]
Thus ;
[tex] \alpha = 45° = \frac{\pi}{4} \\ [/tex]
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[tex]l = 13 \times \frac{\pi}{4} \\ [/tex]
[tex]l = \frac{13}{4} \pi \: \: km \\ [/tex]
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