Chapter 5.6, Problem 12P

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.

$y\text{'}\text{'}-y=u_1(t)-u_2(t);$ $y(0)=12,$

$y\text{'}(0)=7;$ $y\text{'}\text{'}(0)=2$,      $y\text{'}\text{'}\text{'}(0)=-9$