Chapter 5.6, Problem 11P

In each of Problems $1$ through $13$, find the solutions of the given initial value problem. Draw the graphs of the solution and of the forcing function; explain how they are related.

$y\text{'}\text{'}+4y=u_{\pi }(t)-u_{3\pi }(t);$ $y(0)=3,$ $y\text{'}(0)=7;$