Differentiation of scalar and vector products

Discussion in 'Math' started by gusmas, Feb 14, 2011.

  1. gusmas

    Thread Starter Active Member

    Sep 27, 2008
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    Hey guys

    I have a Tutorial that I need to hand in , in 2 weeks but I am stuck with the following problem:

    The question Is: "question.jpg"
    The answer according to the notes the lecturer gave us is: 2-2u-9u^2.

    When I do the math(see atttached document: "workings.jpg" My answer differ slightly and I can not see the problem in my workings, so hoping you guys can maybe spot a problem or if not maybe the answers he gave us is not correct.(even though I asked him and he could not give me a 100% on a yes or no).
     
  2. Georacer

    Moderator

    Nov 25, 2009
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    Is any one of i or j the imaginary unit?
     
  3. Papabravo

    Expert

    Feb 24, 2006
    10,137
    1,786
    I don't think so. ijk are commonly used basis vectors for the Cartesian coordinate system.

    I like your result. The sign of the u^2 term in the dot product is positive. I don't see how he got the negative sign.
     
    Last edited: Feb 14, 2011
  4. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
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    If i, j, and k are the usual Cartesian unit vectors and your F \cdot G is the usual dot product, then I get the same answer you do.
     
  5. Georacer

    Moderator

    Nov 25, 2009
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    Oh, the Cartesian basis vectors, I see. But it seems I 'm a bit too late, as this is already answered.
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    Well clearly eight eyeballs are better than two
     
  7. gusmas

    Thread Starter Active Member

    Sep 27, 2008
    239
    0
    Wow guys/girls thanks for all the response to this thread, really appreciate it. I don't know how this forum work, but there were more questions to that tutorial , which the answers that were given with it does not agree with my answers, is it ok if I scan in my work and post it in this thread, so you guys can take a look and see if I made a mistake somewhere? I wont ask anyone to work out the problem for me ,I will do all the work. Just want to know if I am on the right path with this work, since a test is coming up aswell and I want to score well in it.

    Thanks
     
  8. Georacer

    Moderator

    Nov 25, 2009
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    Of course you can post your work for verification.

    If it is purely math, leave it in the Math forum. Otherwise it might be better suited in the Homework Help section.
     
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