Răspuns:
[tex]aria \: disc = \pi \times {r}^{2} \\ lungimea \: cerc = 2\pi \times r \\ \\ 5. \: l \: cerc = 6\pi \: cm \\ 2\pi \times r = 6\pi \: cm ) \div \pi \\ 2 \times r = 6 \\ r = 6 \div 2 \\ r = 3 \: cm \\ aria \: disc = \pi \times {3}^{2} = 9\pi \: {cm}^{2} \\ \\ 6. \: aria \: disc = 144\pi \: {cm}^{2} \\ \pi \times {r}^{2} = 144\pi \: {cm}^{2} ) \div \pi \\ {r}^{2} = 144 = > r = \sqrt{144} = 12 \: cm \\ l \: cerc = 2\pi \times 12 = 24\pi \: cm[/tex]
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