Define $I = \begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix}$. For each part below, compute $I + A + \frac{A^2}{2!} + \frac{A^3}{3!} + \frac{A^4}{4!}$ with the given $A$, where by $A^k$ we mean the product $AA\cdots A$ consisting of $k$ copies of $A$.
(a) $A = \begin{pmatrix} -1 & 0 \\ 0 & 3 \end{pmatrix}$.
(b) $A = \begin{pmatrix} 2 & 1 \\ 0 & 2 \end{pmatrix}$.