Sifting Subsets for Subspaces In each of Problems 1-3, decide whether the given subset W of the

Question:

Sifting Subsets for Subspaces In each of Problems 1-3, decide whether the given subset W of the vector space V is or is not a subspace of V. If not, identify at least one requirement that is not satisfied?
1. V = R2, W = {(x, y) | y = 0}
2. V = R3, W = {(x, y) | x2 + y2 = 1}
3. V = R3, W = {(x1, x2, x3) | x3 = 0}