Answer:
Option C
Step-by-step explanation:
Here,
[Taking 'A' = 'a']
[tex]a \: = \: 4\pi {r}^{2} [/tex]
Then for 'r',
[tex] = > 4\pi {r}^{2} = a[/tex]
[tex] = > {r}^{2} = \frac{a}{4\pi} [/tex]
[tex] = > r = \sqrt{\frac{a}{4\pi} }[/tex]
[tex] = > r = \frac{1}{2}\sqrt{ \frac{a}{\pi} } [/tex]
Hence,
Option C is correct .
