Explicație pas cu pas:
[tex]L = 2\pi \: r[/tex]
[tex]A =\pi {r}^{2} [/tex]
1) r = 2,5
[tex]L = 2\pi \: r = 2\pi \times 2.5 = 5\pi[/tex]
[tex]A =\pi {r}^{2} = \pi(2.5)^{2} = 6.25\pi[/tex]
2)
[tex]L = 4\pi = > 2\pi \: r = 4\pi = > r = 2[/tex]
[tex]A =\pi {r}^{2} = {2}^{2}\pi = 4\pi [/tex]
3)
[tex]A =\pi {r}^{2} = 64\pi \\ = > {r}^{2} = 64 = > r = 8[/tex]
[tex]L = 2\pi \: r = 2\pi \times 8 = 16\pi[/tex]
