[tex]\text{The standard form of the circle:}\\\\(x-h)^2+(y-k)^2=r^2\\\\\text{h and k are the x and y coordinates of the center}\\\\\text{We have:}\\\\\text{the center}\ (0;\ 3)\to h=0;\ k=3\\\\\text{the radius}\ r=7\\\\\text{substitute:}\\\\(x-0)^2+(y-3)^2=7^2\\\\x^2+(y-3)^2=49[/tex]