1 2 3 5 -7 2 0 1 2 6 1 3 The matrix is not in REF because: 0 0 0 0 0 0 0 0 0 0 0 1 O There is no leading 1 in Row 3. O There is a 2 in the fourth column above the leading 1 in Row 4. O This matrix is actually in REF. The row of all zeros is not at the bottom