Answer
Because two rows are equal, through replacement we get a row of 0s. We then reduce the matrix to echelon form $U$ using only replacements and interchanges. Then $\det A=(-1)^p \det U=(-1)^p\prod_{i=1}^n u_{ii}$ and one of the $u_{ii}$ is $0$, so $\det A=0$
Work Step by Step
Because two rows are equal, through replacement we get a row of 0s. We then reduce the matrix to echelon form $U$ using only replacements and interchanges. Then $\det A=(-1)^p \det U=(-1)^p\prod_{i=1}^n u_{ii}$ and one of the $u_{ii}$ is $0$, so $\det A=0$
