Find the general solution of \begin{equation}
y''+12y'+9y=0
\end{equation}
Solve:
\begin{equation}
4r^2+12r+9r=0\\
(2r+3)^2=0\\
r_1=r_2=-\frac{3}{2}\\
Thus, \qquad \qquad \qquad \qquad \qquad\\
y=c_1e^{-\frac{3t}{2}}+c_2te^{-\frac{3t}{2}}
\end{equation}
