Let W and W′ be two finite dimensional subspaces of an inner product space such that dim(W) < dim(W′). Prove that there is a nonzero vector x in W′ orthogonal to W.
This should be an easy problem but I'm stuck. Here's what I got: find a basis S for the intersection of W and W′ and then apply Gram-Schmidt. Then extend it into S′ a basis for W′ and Gram-Schmidt again. There should at least be one vector in S′ but not S. Call it x. It should be orthogonal to W. But I don't know how to show that.
OK. After some example in lower dimensional space, I found out the reason I'm stuck is because my claim is not true. We might have to do this using dimension.