ANSWER:
[tex]x^2+y^2=13[/tex]STEP-BY-STEP EXPLANATION:
We have that the equation of the circle is given by the following equation
[tex]\begin{gathered} (x-h)^2+(y-k)^2=r^2 \\ \text{where (h, k) is the center and r is the radius} \end{gathered}[/tex]Replacing:
[tex]\begin{gathered} (x-0)^2+(y-0)^2=\sqrt[]{13}^2^{} \\ x^2+y^2=13 \end{gathered}[/tex]