The recurrence $a_n = 2a_{n-1} + 0.5a_{n-2}$ can be written in matrix form as: $\begin{pmatrix} a_n \\ a_{n-1} \end{pmatrix} = A \begin{pmatrix} a_{n-1} \\ a_{n-2} \end{pmatrix}$

Which is the correct companion matrix $A$?