x1 - x2 + x3 = 1,
2x1 +2x2 + x3 = 5+1,
x1 + 3x2 - x3 = 4+2,
x1 + 7x2 - 2x3 = 10-1
augmented matrix is (using L for lambda)
(You can imagine a dotted line between 3rd and 4th columns if you want to seperate the coefficents on LHS from constants on RHS)
1, -1, L, 1
2, 2, 1, 5L+1
1, 3...