1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook