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Math Help - cross products

  1. #1
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    cross products

    Find the cross product of the vectors i + j - k and i - j + k

    any help with this one please.
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  2. #2
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    This is pretty standard. Do you know the formula for the cross product of two vectors?
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  3. #3
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    Quote Originally Posted by rcmango View Post
    Find the cross product of the vectors i + j - k and i - j + k

    any help with this one please.
    Let a = <1, 1, -1>, b = <1, -1, 1>

    Then,

    a x b = [[0, -a_3, a_2], [a_3, 0, -a_1], [-a_2, a_1, 0]]*[[b_1], [b_2], [b_3]], where the * is matrix multiplication.

    And thus we have:

    a x b = [[0, 1, 1], [-1, 0, -1], [-1, 1, 0]]*[[1], [-1], [1]]

    = <0, -2, 0>

    You can also compute the cross product using determinants, which some people find easier. I personally find this much faster.
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