Determine whether the given vectors are orthogonal, parallel, or neither.
(a) a = (9, 3), b = (-2, 6)
orthogonal
parallel
neither
(b) a = (4, 7, -2), b = (3, -1, 7)
orthogonal
parallel
neither
(c) a = -12i + 4j + 8k, b = 9i - 3j - 6k
orthogonal
parallel
neither
(d) a = 3i - j + 3k, b = 3i + 3j - 2k
orthogonal
parallel
neither