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Thread: Cross Product negative or positive

  1. #1

    Cross Product negative or positive

    Just doing some revision, making sure I know how to answer all the questions found on my mock exam paper.

    I'm a little lost, trying to work out whether my vector results I J K are positive or negative because I calculate it to be positive but having looked at my exam result sheet it's negative and I checked to see if the exam sheet result was orthogonal and it was, so I must be going wrong somewhere.

    Untitled.jpg 11i is read as -11i on my mock exam results, can someone tell me where I'm going wrong? Thanks!

  2. #2
    Elite Member stapel's Avatar
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    Quote Originally Posted by Drunvalo View Post
    Just doing some revision, making sure I know how to answer all the questions found on my mock exam paper.

    I'm a little lost, trying to work out whether my vector results I J K are positive or negative because I calculate it to be positive but having looked at my exam result sheet it's negative and I checked to see if the exam sheet result was orthogonal and it was, so I must be going wrong somewhere.

    Untitled.jpg 11i is read as -11i on my mock exam results, can someone tell me where I'm going wrong? Thanks!
    I think (?) you're computing the determinant by using minors and cofactors, but you're missing the "plus/minus" signs between the terms on the right-hand side of your first "equals" sign after the original determinant. I suspect your "minus" signs are lurking there....

  3. #3
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    Code:
    |1   3|
    |4   1|   =   1*1 - 3*4   =   -11
    Last edited by Subhotosh Khan; 05-05-2014 at 02:26 PM.
    “... mathematics is only the art of saying the same thing in different words” - B. Russell

  4. #4
    Quote Originally Posted by Subhotosh Khan View Post
    Code:
    |1   3|
    |4   1|   =   1*1 - 3*4   =   -11
    mind = blown. Wow, I can't believe I didn't realize that. Thank you, very much.

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