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Math Help - Vectors Question

  1. #1
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    Vectors Question

    Ok, so i have Vectors A + B + C = 0

    From this, am i right in thinking that it forms an equilateral triangle? Or is that incorrect?

    I need to use the above to find the answer to a.b + b.c + c.a
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  2. #2
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    The three vectors form a triangle, but you are by no means guaranteed that it is an equilateral triangle. As for your answer, what kind of an answer are you to compute? I don't think you're going to be able to find the exact number.
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  3. #3
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    Quote Originally Posted by Mcoolta View Post
    Ok, so i have Vectors A + B + C = 0
    From this, am i right in thinking that it forms an equilateral triangle? Or is that incorrect?
    I need to use the above to find the answer to a.b + b.c + c.a
    It seems as if you have simply posted only a piece of a problem.
    If you post the complete question, we may be able to help you with it.
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  4. #4
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    Using three unit vectors a, b, c, so that A+B+C = 0, find a.b + b.c + c.a

    Thats all that was given in the question.
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  5. #5
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    Before, you left out a most important word: UNIT.
    Because they are units, recall that \left\| A \right\|=1

    \begin{gathered}<br />
  \left( {A + B + C} \right) \cdot \left( {A + B + C} \right) = 0 \hfill \\<br />
  \left\| A \right\|^2  + \left\| B \right\|^2  + \left\| C \right\|^2  + 2A \cdot B + 2A \cdot C + 2C \cdot B = 0 \hfill \\ <br />
\end{gathered}
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  6. #6
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    Ah ok, thanks. So i get a.b + b.c + c.a = -3/2 ?
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  7. #7
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    Yes.
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