Answer
$A^{-1}$ does not exist
Work Step by Step
Given: $A=\begin{bmatrix}
0 & 1 & 0\\
0& 0 & 1\\
0 & 1 & 2
\end{bmatrix}$
The matrix has one column of all zero elements and furthermire $rank(A)=0 \lt 3=n$.
According to the Theorem: Matrix A is invertible if and only $rank(A)=n$.
Hence here, the matrix is not invertible, so it doesn't have the inverse.
