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I 1st year linear algebra question

  1. Jan 19, 2017 #1
    given P(-1,1,2), Q(-3,0,4), R(3,2,1), find an equation of the line through P that is parallel to the line through Q and R.

    All the words after the given three points really confuse me and I just need some help on where to start to tackle this problem.

  2. jcsd
  3. Feb 19, 2018 #2


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    Geometrically, you need to find a line going through P. But not just any line will do - it's gotta be parallel to another line. Which line does it need to be parallel to? The one going through Q and R. So, Step One would be to find the line going through Q and R.
    Last edited by a moderator: Feb 21, 2018
  4. Feb 21, 2018 #3


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    since 2 days have passed, maybe more detailed help is warranted. basic facts: point - point = vector parallel to the line through the two points. point + vector = another point on the line through the first point and having the given direction vector.

    In general you can subtract 2 points and get a direction vector; and you can add a vector to a point to get another point on the line through the given point and parallel to the given vector.

    oops a year has passed!
    Last edited: Feb 21, 2018
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