Answer
See work
Work Step by Step
Because $\mathrm{A}$ is not invertible, there is a nonzero vector $\mathrm{v}$ in $R^{n}$ such that $\mathrm{Av}=0$. Place n copies of $\mathrm{v}$ into an $\mathrm{nn}$ matrix $\mathrm{B} .$ Then $A B=A[v \ldots v]=[A v \ldots A v]=0$
