The correct option is A ∣∣[→a,→b,→c]∣∣∣∣→a×→b+→b×→c+→c×→a∣∣
The vector equation of the plane passing through points →a,→b,→c is
r.(→a×→b+→b×→c+→c×→a)=[→a,→b,→c]
Therefore, the length of the perpendicular from the origin to this plane is given by
∣∣[→a,→b,→c]∣∣∣∣→a×→b+→b×→c+→c×→a∣∣