Use the given general solution to find a solution of the differential equation having the given initial condition. Sketch the solution, the initial condition, and discuss the solution's interval of existence.
$$
\begin{aligned}
&y^{\prime}+4 y=\cos t, y(t)=(4 / 17) \cos t+(1 / 17) \sin t+C e^{-4 t}, \\
&y(0)=-1
\end{aligned}
$$