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Homework Help: Exam question t/f 2

  1. Sep 13, 2012 #1

    Mdhiggenz

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    1. The problem statement, all variables and given/known data

    I just remembered another question that I wasn't to sure about

    1) if n1xn2 does not intersect the plan then n1xn2=0
    I chose false for this one.

    thoughts?



    2. Relevant equations



    3. The attempt at a solution
     
    Mdhiggenz, Sep 13, 2012
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  3. Sep 13, 2012 #2

    voko

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    What are n1 and n2, and what is "the plan"?
     
    voko, Sep 13, 2012
  4. Sep 13, 2012 #3

    Mdhiggenz

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    Plane* sorry, n1, and n2 and vectors.
     
    Mdhiggenz, Sep 13, 2012
  5. Sep 13, 2012 #4

    voko

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    What plane is this? n1 x n2 is a vector, and for any given vector there are infinitely many planes it does not intersect.
     
    voko, Sep 13, 2012
  6. Sep 13, 2012 #5

    Mdhiggenz

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    Its a true or false question, don't know what else to tell you.
     
    Mdhiggenz, Sep 13, 2012
  7. Sep 13, 2012 #6

    voko

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    What is "the" plane in the question? Or was that really "a" plane?
     
    voko, Sep 13, 2012
  8. Sep 13, 2012 #7

    Mark44

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    I'm guessing that n1 and n2 are vectors in the plane, and "intersect" means that it (n1 x n2) intersects at a single point.
     
    Mark44, Sep 13, 2012
  9. Sep 13, 2012 #8

    Mdhiggenz

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    Indeed Mark.
     
    Mdhiggenz, Sep 13, 2012
  10. Sep 13, 2012 #9

    LCKurtz

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    You could tell us the complete and exact wording of the question. I have read up through post #8 and I still have no idea what this is about.
     
    LCKurtz, Sep 13, 2012
  11. Sep 13, 2012 #10

    Mdhiggenz

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    Honestly that is exactly how the question was worded.
     
    Mdhiggenz, Sep 13, 2012
  12. Sep 13, 2012 #11

    Mark44

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    Since you're going by what might be an imperfect memory of the problem statement, let's assume that it was as I said.

    IOW, n1 and n2 are vectors in a plane. If n1 X n2 does not intersect the plane at a single point, then n1 X n2 = 0.
     
    Mark44, Sep 13, 2012
  13. Sep 13, 2012 #12

    Mdhiggenz

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    Ugggg why put true or false on a math exam....
     
    Mdhiggenz, Sep 13, 2012
  14. Sep 13, 2012 #13

    LCKurtz

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    What a poorly worded question then. Vectors don't intersect planes. Lines with the given vector as a direction vector might. It would better be stated as the contrapositive: If ##\vec n_1 \times \vec n_2 \ne \vec 0## a line with that direction vector intersects the plane in exactly one point.
     
    LCKurtz, Sep 13, 2012
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