The xy-plane cuts the sphere x2+y2+z2−2x−4y+6z−4=0 in a circle, the radius of which is

Given sphere is  x2+y2+z2−2x−4y+6z−4=0Since it cots the ry-plane where z:0, equation of circular section is x2+y2+z2−2x−4y−4=0The radius of the circle is 1+4−(−4)=9=3