(a) Prove that the only subspaces of R1 are R1 and the zero subspace.
(b) Prove that a subspace of R2 is R2, or the zero subspace, or consists of all scalar multiples of some fixed vector in R2. (The last type of subspace is, intuitively, a straight line through the origin.)
(c) Can you describe the subspaces of R3?