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Homework Help: 3d Point Coordinates

  1. Feb 2, 2006 #1
    As part of a larger question, i need to find a point the following line goes through:

    r = -i + 2j + k + t(i-2k)

    I have rearranged it into an alternative form (as per my notes) as

    r = (t-1) i + 2j + (1-2t) k

    i am supposed to be able to find a point the line passes through from this but i just cant see it, can someone help me out?
  2. jcsd
  3. Feb 2, 2006 #2


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    What happens when t=0 or t=1?
  4. Feb 2, 2006 #3
    see that was what i was trying to think in terms of...but i couldn't see how there were two "limiting vectors" that defined the line.

    if t=0 you get


    and if t=1


    i cant help but think that these are significant somehow...
  5. Feb 2, 2006 #4
    Those are the position vectors of the two points, for t=0 and t=1, through which the line described by r passes.
  6. Feb 2, 2006 #5
    ah i think i get it. thank you very much for the help.
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