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Homework Help: 4th Vertex in a 3D Parallelogram

  1. Nov 28, 2013 #1
    1. The problem statement, all variables and given/known data
    Let P, Q, and R be the vertices of a parallelogram with adjacent sides PQ and PR. Find the other vector S.
    P (2, 0 ,-1), Q (-2, 4, 1), R (3, -1, 0)

    2. Relevant equations
    PR = QS
    PQ = RS

    3. The attempt at a solution
    I took the two equations and solved both of them, getting (-1, 3, 2) for S by making the coordinates of S into x, y, and z and solving the equations. However, my answer doesn't seem to be correct. Why am I wrong? Thank you in advance.
  2. jcsd
  3. Nov 28, 2013 #2


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    Homework Helper

    Hi Temp0! :smile:
    I don't understand your method, but your result seems correct. :confused:

    (are you sure it isn't "with adjacent sides PQ and QR"?)
  4. Nov 28, 2013 #3


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    Homework Helper

    yeah... I get S = (-1,3,2) also.
  5. Nov 28, 2013 #4
    Just checked, nope, PQ and PR... I think it might be a mistake in the book ;_;
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