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Homework Help: Understanding how to solve this set

  1. Feb 12, 2012 #1
    1. The problem statement, all variables and given/known data
    Hello guys, I have a physic class this session and I'm self-teaching myself most of the material. It's going not too bad so far but I have come across a form of solving I have not seen before and would like to understand how it works. I have the data and the answer, I just don't know how to get the answer from the equation. This is the last part of a problem I have to solve that deal with the moment of a force about an edge.

    2. Relevant equations
    For easier format, here is a picture:
    http://unwantedcreations.com/img/physic_1.png [Broken]
    First line is λ of the edge
    Second line are the coordinate of the point of application of force F
    third line are the components x, y and z of the force F.

    in case you don't get it at all, here is the problem and solution:

    3. The attempt at a solution

    Ok so I think I get where -25.363 come from, if you take 0.99228 * -1.8 * 14.2 it does make -25.363, but where does -10.5678 comes from? No idea.

    Thank you for your time guys.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Feb 12, 2012 #2


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    Science Advisor
    Homework Helper

    hi ucflap! :smile:
    it's 0.124035*6*14.2 …

    to calculate a determinant, you multiply one element from each row and column, ie you zig-zag in every possible way

    there are only two zig-zags that don't include a 0, and 0.124035*6*14.2 is one of them :wink:

    (to see why it's minus, look up a book or wikipedia on determinants)
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