Interesting problem. As was mentioned earlire, the space generated by A, B, and C will be xA+yB+zC. The format in which A, B, and C are written down is totally irrelevant - you can write them in a 2x2 square, but you could also write them down (in any order that's convenient) as a usual 4-element vector. Writing them in the more familiar form may make it easier. It's possible the three vectors lie in the same plane (you'd have to check), but it's more likely they generate a 3d subspace of R^4.