SOLUTION
Notice that the center of the circle is (0,0)
The radius of the circle is r=4
Recall that the equation of a circle with center (h,k) and radius r is:
[tex](x-h)^2+(y-k)^2=r^2[/tex]
Using the value, the equation of the circle is
[tex]\begin{gathered} (x-0)^2+(y-0)^2=4^2 \\ x^2+y^2=16 \end{gathered}[/tex]
Therefore the equation of the circle is:
[tex]x^2+y^2=16[/tex]
