A Subset that is Not a Subspace It is certainly not the case that all subsets of R" are subspaces. To show that a subset U of R" is not a subspace of R", we can give a counterexample to show that one of (SO), (S1), (S2) fails. Example: Let U = = { [2₁₂] € R² | 1 2=0}, that is, U consists of the vectors [21] € R² such that ₁x2 = 0. Give an example of a nonzero vector u € U: 0 u 0 #1x2 =