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Math Help - Perpendicular Vector Resolute

  1. #1
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    Perpendicular Vector Resolute

    PLEASE HELP



    Me and my friends keep getting 1/9(13i - 20j - 23k) for this question and can't work out why the sign is incorrect, I am investigating whether or not it is a typo but am wondering what you guys think the answer is?

    Also sorry if this is the wrong board, I wasn't sure if it was algebra or geometry...
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  2. #2
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    Re: Perpendicular Vector Resolute

    first, the dot product of (1/9)(13i- 20j- 23k) and (2i- j+ 2k) is (1/9)(26+ 20- 46)= 0 so that IS perpendicular to 2i- j+ 2k to begin with!

    On the other hand, the dot product of (1/9)(13i+ 20j- 23k) and (2i- j+ 2k) is (1/9)(26- 20- 46) is NOT 0 so they are not perpendicular so D is the answer in the book it is not correct.
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  3. #3
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    Re: Perpendicular Vector Resolute

    [B[/B]
    Quote Originally Posted by AndrewP View Post
    PLEASE HELP



    Me and my friends keep getting 1/9(13i - 20j - 23k) for this question and can't work out why the sign is incorrect, I am investigating whether or not it is a typo but am wondering what you guys think the answer is?

    Also sorry if this is the wrong board, I wasn't sure if it was algebra or geometry...
    Follow Math Help Forum on Facebook and Google+

  4. #4
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    Re: Perpendicular Vector Resolute

    Your answer is correct. Apologies for my earlier incorrect reply.
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