\[\begin {array} {1 1} (1)\;x^2+y^2-4x-6y-16=0 & \quad (2)\;x^2+y^2-4x-6y-20=0 \\ (3)\;x^2+y^2-4x-6y-12=0 & \quad (4)\;x^2+y^2+4x+6y-12=0 \end {array}\]