hello
to solve this problem, we can simply use the formula of area of a circle.
[tex]\begin{gathered} A_{circle}=\pi r^2 \\ \pi=\text{constant} \\ r=\text{?} \end{gathered}[/tex]let's input the values into the formula
[tex]\begin{gathered} A_{\text{circle}}=\pi r^2 \\ 1=\pi r^2 \\ \text{divide both sides by pi} \\ \frac{1}{\pi}=r^2 \\ \text{take the square root of both sides} \\ r^2=\frac{1}{\pi} \\ r=\sqrt[]{\frac{1}{\pi}} \end{gathered}[/tex]