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Math Help - Cross product.

  1. #1
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    Cross product.


    Q17: Given: a = i + j + k, a. b = 1 and a b = j - k. Then, b is equal to
    A. -2i
    B. 2i + k
    C. 3j
    D. i
    how?
    Last edited by mr fantastic; February 11th 2011 at 01:27 AM. Reason: Re-titled, deleted excessive ?'s in post, moved to correct subforum.
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  2. #2
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    An idea might be to start by defining \displaystyle \mathbf{b} = x\mathbf{i} + y\mathbf{j} + z\mathbf{k} so that you can get expressions for \displaystyle \mathbf{a}\cdot\mathbf{b} and \displaystyle \mathbf{a}\times\mathbf{b}, which you then should be able to solve simultaneously for \displaystyle x,y,z...
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