Determine whether the given vectors are orthogonal, parallel, or neither.

(a) u = (−5, 4, −2),    v = (3, 4, −1)

(b) u = 9i − 6j + 3k,    v = −6i + 4j − 2k

(c) u = (c, c, c),    v = (c, 0, −c)