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The points A, B and C have position vectors a=(2,1,2) b=(-3,2,5) and c=(4,5,-2) respectively, with respect to a fixed origin. The point D is such that ABCD, in >that order, is a parallelogram.

  1. Find the position vector of D
  2. Find the position vector of the point at which the diagonals of the >parallelogram intersect.
  3. Calculate the angle BAC, giving your answer to the nearest tenth of a degree.
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Have you drawn it? –  Berci Oct 10 '12 at 1:16
    
$a,b,c$ determine a plane. So you work on this plane. –  Sigur Oct 10 '12 at 1:41
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