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Please help me just understand what this question is asking of me (linear algebra)

  1. Feb 20, 2012 #1
    1. The problem statement, all variables and given/known data

    So we are given the equation of a line and asked to do a bunch of stuff with it. When I get to the following question, I just don't understand what it is asking.

    The line:

    L=(2,2,5)+t(2,-1,1), where t is an element of the reals

    Question:

    Let S be the the line segment consisting of the points on L whose coordinates are all nonnegative (that is, S is the intersection of L with the first octant). Find the vector equation of S.

    2. Relevant equations



    3. The attempt at a solution

    I don't quite understand what they're asking.. I know that at a point, all of the coordinates of the points on line L will be negative. But are they asking us to simply find a vector from the origin to the point at which this happens? Or are they asking us to find a vector along the line that represents all of these points (which doesn't make sense to me because in my mind that vector would be infinitely long).

    Thanks!
     
  2. jcsd
  3. Feb 20, 2012 #2
    Re: Please help me just understand what this question is asking of me (linear algebra

    Could it just be a restriction on t?
     
  4. Feb 20, 2012 #3
    Re: Please help me just understand what this question is asking of me (linear algebra

    I was actually thinking that too.. but it seems too simple to be worth 4 points in my assignment.
     
  5. Feb 20, 2012 #4

    SammyS

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    Re: Please help me just understand what this question is asking of me (linear algebra

    Is it standard practice to parametrize the segment so that when the scalar parameter spans the interval [0, 1], the vector parametrization spans the entire segment ?
     
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