It's a problem from MIT 18.06 14 Spring Exam1. The vectors are all 4 dimensional. I suppose that there are infinitely many such space orthogonal to that fixed subspace spanned by those 2 independent vectors (let's call them v and w). But 2 dimensional subspace that contains all and only vectors orthogonal to those 2 vectors is a different thing. It's hard to visualize this problem in 4 dimensional space so I tried reasoning in 3 dimensional space. There are infinitely many 2 dimensional plane orthogonal to the subspace spanned by z-axis. But only the x-y plane contains all vectors orthogonal to z-axis. I believe it's also true for higher dimension (such space is unique).
OK, but I don't know how to extend this 3 dimensional case to 4 dimensional space to convince myself. Any help?