Multiply row (2) of the first matrix by $-2$ to get the second matrix. To reverse this operation, divide row (2) of the second matrix by $-2$ to get the original matrix.
Work Step by Step
Recall from the bottom of page 6 and the top of page 7 that all elementary row operations are reversible. Moreover, there are only three such operations: (1) swapping two rows, (2) multiplying a row by a nonzero constant, and (3) adding a constant multiple of one row to another row.