The quaternion group is the group G = {1, -1, i, -i, j, -j, k, -k} with identity element 1 and defined by the following rules:
(-1)^2 = 1,
i^2 = j^2 = k^2 = -1,
ij = k, jk = i, ki = j,
ji = -k, kj = -i, ik = -j,
(-1)x = -x = x(-1) for all x ∈ G.
(a) Show that the subgroup H = {1, -1} is normal in G.
(b) Show that G/H ≈ Z2 ⊕ Z2.