Question:
If $A$ is a singular matrix, then $A(\operatorname{adj} A)=$____________
Solution:
As we know that, $A(\operatorname{adj} A)=|A| I$.
But it is given that $A$ is a singular matrix
Thus, $|A|=0$
Therefore, $A(\operatorname{adj} A)=0 I=O$, where $O$ is the zero matrix.
Hence, if $A$ is a singular matrix, then $A(\operatorname{adj} A)=\underline{O}$.