Augmented matrix in row echelon form:

x1|x2|x3|b

1 -3 7 1

0 1 4 0

0 0 0 1

x1= 1 + 3x2 - 7x3

x2= - 4x3

x3= 1

Is this the solution set?

Matrix #2

1 0 8 -5 6

0 1 4 -9 3

0 0 1 1 2

x1 = 6 -8x3 + 5x4

x2 = 3 - 4x3 + 9x4

x3 = 2 -x4

x4 = ?

I have trouble with this one especially.

Edit: Okay I think I got matrix #2. x4 is a free variable and we can assign it the arbitrary value "t". In this case the solution set is:

x1 = 6 -8x3 + 5t

x2 = 3 - 4x3 + 9t

x3 = 2 - t

x4 = t

Yes?