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Homework Help: Vector product

  1. Dec 2, 2008 #1
    1. The problem statement, all variables and given/known data

    A = -3i + 4j and B = 2i + 3j

    so I want to find AxB

    2. Relevant equations



    3. The attempt at a solution

    what I got is -9k + 8k, which is -k but the answer solution says it's -17k ?
     
  2. jcsd
  3. Dec 2, 2008 #2

    G01

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    You are missing a negative sign on the 8. Remember that when you take the cross product of two vectors, A and B, in the x-y plane you will get:

    [tex](A_xB_y-A_yB_x)\hat{k}[/tex]

    You are missing the minus sign in the above equation.
     
  4. Dec 2, 2008 #3

    G01

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    EDIT: This post refers to a post deleted by the OP.


    The i x i and j x j terms are zero by definition. You then have:

    -9(i x j)+8(j x i)

    Remember that the cross product anticommutes. So if ixj=k. What does this mean for j x i?
     
    Last edited: Dec 2, 2008
  5. Dec 2, 2008 #4
    jxi is k?
     
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