O is the centre, AB and BC are two diagonals of the adjacent faces of a rectangular box. If angles AOB, BOC and

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Q 1287701687.     O is the centre, AB and BC are two diagonals of the adjacent faces of a rectangular box. If angles AOB, BOC and COA are θ, ϕ and ψ respectively, then cos θ + cos ϕ + cos ψ is equal to
A

0

B

-1

C

1

D

1.5

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