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Homework Help: Vector Multiplication

  1. Feb 12, 2007 #1
    1. The problem statement, all variables and given/known data

    "PRQSTU is a regular hexagon of side 2 units. PQ,QR and RS represent vectors a, b andc respectively. Find the value of a.(b + c)

    The hexagon is a regular hexagon starting at the far left (ie pointing left) with P then anti clockwise through U at the top left.

    2. Relevant equations

    None that I can think of.

    3. The attempt at a solution

    I really don't know where to start. I've guessed that a (PQ) = -c. But I don't know where to go from there and now I'm really confused.

    Any help greatly appreciated.
  2. jcsd
  3. Feb 12, 2007 #2


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    You must be drawing a pretty horrid picture of a hexagon to be guessing that a=(-c). If you draw a neat picture you will probably realize there is a special angular relationship between a and b+c. You could also just tough it out and compute the components of the vectors a, b and c, since you know their lengths and the angles between them.
  4. Feb 12, 2007 #3
    Thanks for the reply.

    I think I realised why I was lost - it's because I was! We haven't been taught this part of vectors yet, and I was looking at a past paper.

    Haha, oops. The picture was already printed for me and I thought that a=(-c). I better stick to diagrams of squares. :)
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