Obtain the general solution of the differential equation $$\frac { \mathrm { d } ^ { 2 } x } { \mathrm {~d} t ^ { 2 } } + 6 \frac { \mathrm {~d} x } { \mathrm {~d} t } + 13 x = 75 \cos 2 t$$ Given that \(x = 5\) and \(\frac { \mathrm { d } x } { \mathrm {~d} t } = 0\) when \(t = 0\), find \(x\) in terms of \(t\). Show that, for large positive values of \(t\) and for any initial conditions, $$x \approx 5 \cos ( 2 t - \phi ) ,$$ where the constant \(\phi\) is such that \(\tan \phi = \frac { 4 } { 3 }\).