4 5 6 7 3 4 5 6 2 3 4 5 1 2 3 4 Multiply row 2 by -1 and add it to row 1 1 1 1 1 3 4 5 6 2 3 4 5 1 2 3 4 Multiply row 3 by -1 and add it to row 2 1 1 1 1 1 1 1 1 2 3 4 5 1 2 3 4 Multiply row 4 by -1 and add it to row 3 1 1 1 1 1 1 1 1 1 1 1 1 1 2 3 4 Multiply row 1 by -1 and add it to row 2 1 1 1 1 0 0 0 0 1 1 1 1 1 2 3 4 Multiply row 1 by -1 and add it to row 3 1 1 1 1 0 0 0 0 0 0 0 0 1 2 3 4 Swap rows 2 and 4 1 1 1 1 1 2 3 4 0 0 0 0 0 0 0 0 Multiply row 1 by -1 and add it to row 2 1 1 1 1 0 1 2 3 0 0 0 0 0 0 0 0 Multiply row 2 by -1 and add it to row 1 1 0 -1 -2 0 1 2 3 0 0 0 0 0 0 0 0 That's in row reduced echelon form. The number of not-all-zero rows is 2, so its rank is 2. Edwin