3) Below are some subsets of Rn. For each subset, determine if it is a subspace. If it is not a subspace, explain WHY it is not a subspace. If it IS a subspace, prove it and find a basis and dimension for the subspace. Under what circumstance is it possible for the union of two subspaces to be a subspace? a) W = {x, y, z | 2x + 3y 4z = 0} b) V = {x, y | xy 0} c) X = {x, y, z | xy = z} d) Z = {a, b, c, d | 2a + 3b = c d and a b + 5c = 3d}