1. The problem statement, all variables and given/known data This is what I've just been tested and I didn't know what to do :( Sorry I can't remember what the question is since the question paper was collected after the test. 2. Relevant equations 3. The attempt at a solution When A is invertible just set up the augmented matrix (A|B) and perform eros until we get the identity matrix on the LHS and X is what's on the RHS. What if A is not invertible?