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Homework Help: Vector proof - four points in space

  1. May 15, 2012 #1
    The problem is: A, B, C, D are any four points in space. If M and N are the mid-points of AC and BD, show that AB + CB + CD = 4MN.

    I'm not quite sure where to start. Could someone please help me?
  2. jcsd
  3. May 15, 2012 #2
    I'm not sure that the problem is correct. Suppose that A,B,C,D are the four corners of a square. In this case, M and N would both be the center of the square. This would make MN=0
  4. May 15, 2012 #3


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    welcome to pf!

    hi nc01! welcome to pf! :smile:
    ?? :confused:

    i think you need an AD in there …

    AB + AD + CB + CD = 4MN :wink:
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