If $ A = \begin{pmatrix} 1 & 3 \\ 2 & 4 \end{pmatrix}$ then show that `A^2-5A-2I_2=O` where $ I_2 = \begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix}$ and $ O = \begin{pmatrix} 0 & 0 \\ 0 & 0 \end{pmatrix}$. Hence find `A^{-1}`