The differential equation of all circles passing through the origin and having their centres on the $x$-axis is
(1) $x ^ { 2 } = y ^ { 2 } + x y \frac { d y } { d x }$
(2) $x ^ { 2 } = y ^ { 2 } + 3 x y \frac { d y } { d x }$
(3) $y ^ { 2 } = x ^ { 2 } + 2 x y \frac { d y } { d x }$
(4) $y ^ { 2 } = x ^ { 2 } - 2 x y \frac { d y } { d x }$
The differential equation of all circles passing through the origin and having their centres on the $x$-axis is\\
(1) $x ^ { 2 } = y ^ { 2 } + x y \frac { d y } { d x }$\\
(2) $x ^ { 2 } = y ^ { 2 } + 3 x y \frac { d y } { d x }$\\
(3) $y ^ { 2 } = x ^ { 2 } + 2 x y \frac { d y } { d x }$\\
(4) $y ^ { 2 } = x ^ { 2 } - 2 x y \frac { d y } { d x }$