I have a matrix 4x4: 1,2,3,4 2,6,6,6 0,0,1,13 0,0,0,1 I need to find determinant. I am getting det=6. When I use online matrix calculator it gives me det=2. I tried reduce second row (2 row - 1(1 row)) and I got det=2 I'm confused. Why calculator gives me different answer?