fleeceman10

1. The problem statement, all variables and given/known data
I think I have broken maths. I am reducing a matrix to row echelon form to find the determinant. The matrix I will show is nearly in the desired form


2. Relevant equations
1 -3 -2 1
0 1 2 -1
0 0 1 -0.8
0 0 1 0


3. The attempt at a solution
As it stands, the determinant is 0.8. However subtracting the 4th row from the 3rd row changes the determinant to -0.8. I thought adding multiples of one row to another left the determinant unchanged. So why hasn't it? Thanks for answers.