 Quote by fleeceman10
What if you do 3rd row - 4th row, replacing 4th row.
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You're not allowed to do that.
You
can replace the 4th row by adding the 3rd row to the 4th row.
You
can't muck about with the row you're replacing (you've multiplied it by -1
)
before you start adding to or subtracting other rows from it.