Which of the following subsets of R3 are actually subspaces?
(a) The plane of vectors (x1,x2,x3) with x1 = 0.
(b) The plane of vectors (x1,x2,x3) with x1 = 1.
(c) The vectors with x1x2x3 = 0.
(d) All vectors that satisfy x1 + x2 + x3 = 0.
(e) All vectors that satisfy x1 + x2 + x3 = 1.
(f) All linear combinations of (1,1,0) and (−2,3,0).
(g) All vectors with x1 ≤ x2.
(h) All vectors with x1 = x2.