# How do you find the inverse of A=((0, 1, 0), (0, 1, -4), (0, 0, 1))?

This matrix has no inverse since its determinant is $0$
$\left\mid \begin{matrix}0 & 1 & 0 \\ 0 & 1 & - 4 \\ 0 & 0 & 1\end{matrix} \right\mid = 0$ since the first column is $0$
Hence $A$ has no inverse.