Let p, qand r be three mutually perpendicular vectors of the same magnitude. If a vector x satisfies equation p x {(x - q) x p} +q x {(x - r) x r} + r x {(x - p) x r} = 0, then x is given by
(a) 1/2 (p + q -2r)
(b) 1/2 (p + q +**r**)
(c) 1/3 (2p + q - r)
(d) 1/3 (2p + q - r)
