If A, B and C are three singular matrices given by then the value of abc is:

If  $$n×n$$ matrix A has only one non-zero element, rank of  A is

If $$I$$ be the $$2×2$$ identity matrix and $$A = \begin{pmatrix} 2 & -1 \\-1 & 2\end{pmatrix}$$, then $$A^2$$ is equal to​