Alright, what the hell does this question mean?
Q. Express in parametric form the set of all solutions x of Ax = Ac where A is the matrix
[(1, -2, 0, 2,) (1, 1, 3, -1)] and c=[1, 2, 3, 7]

For the matrix A, I got the reduced row echelon form as [(1, 0, 2, 0) (0, 1, 1, -1)] So the linear equation would be x_1 + 2x_3 = 0 and x_2 + x_3 -x_4=0. So [x_1, x_2, x_3, x_4] = [x_1-2x_3, x_4-x_3, x_3, -x_2-x_3]. But then since x_3 is the free variable, it would be wrong to set it up as x_3[0, 0, 1, 0] right? Or am I supposed to multiply Ac first? I just don't get the question.