Consider the system $\begin{pmatrix} a_n \\ a_{n-1} \end{pmatrix} = M \begin{pmatrix} a_{n-1} \\ a_{n-2} \end{pmatrix}$. If the eigenvalues of $M$ are $\lambda_1 = 3$ and $\lambda_2 = -2$, what is the trace of $M$?