4. A mass-spring system subject to periodical forcing 1s modeled by the differential equation: y" + 4y' + 4y = 2 cos(t) + sin(t), (a) (5 points) Find the particular solution corresponding to the external force. (b) (5 points) Find its amplitude, frequency and phase shift from previous part. Hint: rewrite the solution to A cos(wt + ). (c) (b points) Find the general solution, and find a solution satisfying: y(0) = 1, /(0) = 2