1. The problem statement, all variables and given/known data Let S be the subspace of R4 given by the solution set of the equations -b + c + d = a - 3 c and -a - 2 d = d = a - c Find an example of a matrix for which S is the nullspace. 2. Relevant equations Ax=0 3. The attempt at a solution I have found that the solution space and hence the null-space can be defined as d(-3,-12,-4,1) so now all thats left is to find a matrix A. that satisfies Ax=0, right? I entered one such matrix, namely A= [4,-1,1,4] and the program says its incorrect, where have i gone wrong? thanks, Michael.