3 The variables \(x\) and \(y\) satisfy the differential equation
$$\frac { \mathrm { d } y } { \mathrm {~d} x } + 4 y = 5 \cos 3 x$$
- Find the complementary function.
- Hence, or otherwise, find the general solution.
- Find the approximate range of values of \(y\) when \(x\) is large and positive.