[tex]L=2*\pi*R \\
a) 10\pi cm=2*\pi*R \\ R= \frac{10 \pi cm}{2\pi}=5 cm \\
b) 8 \pi \sqrt{2} cm = 2*\pi*R \\ R=\frac{8 \pi \sqrt{2} cm}{2\pi}=4 \sqrt{2} cm \\
c) 2 \pi \sqrt{5}cm =2*\pi*R \\ R= \frac{2 \pi \sqrt{5} cm}{2 \pi}= \sqrt{5} cm \\
d) 5 \pi cm=2*\pi*R \\ R= \frac{5 \pi cm}{2\pi}= \frac{5}{2} cm = 2,5 cm [/tex]