The gradient of a curve \(C\) is given by \(\frac { \mathrm { d } y } { \mathrm {~d} x } = \frac { \left( x ^ { 2 } + 3 \right) ^ { 2 } } { x ^ { 2 } } , x \neq 0\).
Show that \(\frac { \mathrm { d } y } { \mathrm {~d} x } = x ^ { 2 } + 6 + 9 x ^ { - 2 }\).
The point \(( 3,20 )\) lies on \(C\).
Find an equation for the curve \(C\) in the form \(y = \mathrm { f } ( x )\).