[tex]a = \pi \: {r}^{2} [/tex]
u take ur known variables and fill them in, pi will be filled in as 3.14
Example:
[tex]153.86 = 3.14 {r}^{2} [/tex]
Then divide both sides by 3.14, after that it should be (number) =r². since it's squared you have to find to square root of both.
Example:
[tex] \sqrt{49} = \sqrt{ {r}^{2} } \\ 7 = r[/tex]
therefore in this example the radius is 7
