Solution
= Solution
Use $A=M$ and $B=N$ from part (a). The proposed unreversed product is
$$
A^{-1}B^{-1}=\begin{pmatrix}-19&15\\14&-11\end{pmatrix},
$$
which differs from the actual inverse $\begin{pmatrix}-25&18\\7&-5\end{pmatrix}$. Both original <matrices> are <invertible matrices>, so this is a valid counterexample. The universally valid order is $\boxed{(AB)^{-1}=B^{-1}A^{-1}}$.