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Homework Help: Dot product computation

  1. Sep 15, 2009 #1
    1. The problem statement, all variables and given/known data

    Which of the following can be computed?

    1. A dot B dot C
    2. A dot ( B dot C )
    3. A dot ( B + C )
    4. 3 dot A

    2. Relevant equations

    3. The attempt at a solution

    I believe that 2 and 3 are the only two that can be computed. Can anyone confirm this? Thanks.
  2. jcsd
  3. Sep 15, 2009 #2


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    Why do you think that? What makes them different from the others?

    I personally disagree with your answer
  4. Sep 15, 2009 #3
    Well I think 4 can't be computed because 3 is not a vector.

    But perhaps 1 can be?

    I'm almost certain 2 and 3 can be.
  5. Sep 15, 2009 #4


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    The 3 isn't that much of a problem. 3 times something is ok for a lot of objects. But how do you compute dot(A)?? Imagine A, B and C are real vectors and try to figure out how you would compute any of these. Only one makes sense.
  6. Sep 15, 2009 #5
    I think the dot product is defined as being a scalar product between two vectors. For this reason I don't think any of the products except number 3 is acceptable:

    A.B.C isnt compatible
    A.(B.C) is A.(Scalar)
    A.(B+C) = A.B + A.C both of which make perfect sense
    3.A is not OK whilst 3A is.
  7. Sep 16, 2009 #6
    Thank you Gregg! Your explanation makes perfect sense to me and is exactly the help I was looking for!
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