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Simple Linear Algrebra find a point

  1. Jun 12, 2008 #1
    1. The problem statement, all variables and given/known data
    Given the two points P(-4,-5,0) and Q(5,5,-3) find the point R that is 1/4 of the way from Q to P.

    2. Relevant equations

    PQ = Point Q- Point P

    3. The attempt at a solution
    I got my direction vector as
    PQ= [9,10,-3]

    but i dont know how to find R

    All i know is that the answer is supopsed to be:

    Im wanted to add 1/4 of my direction vector PQ to my point q but this doesnt give me the right answer
  2. jcsd
  3. Jun 12, 2008 #2


    User Avatar

    Your vector is from P to Q. You want a vector from Q to P (so, QP=[-9,-10,3]).
    Then, R = Q + 1/4*QP.
  4. Jun 12, 2008 #3
    You are on your way to the right answer!
    When you calculate your direction vector [tex] \vec{PQ} [/tex] you actually get a vector which starts at point (0.0) and ends at the vector coordinates you get which in your case are (9,10,-3)
    But your point Q is not (0,0), isn't it?
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