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Help with squaring geometry help

  1. Sep 17, 2003 #1
    x and y are vectors

    If |x|=11 and |y|=23 and |x-y|=30, find |x+y|?

    I tried but I couldn't get it, any hints out there guys?
     
  2. jcsd
  3. Sep 17, 2003 #2

    Hurkyl

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    Try squaring everything.
     
  4. Sep 17, 2003 #3
    I did

    |x|^2 + |y|^2 = |x+y|^2

    Then |x+y|=25.6 units

    But my book's answer says 16 units...I dont get it
     
  5. Sep 17, 2003 #4

    Hurkyl

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    That formula only works when x and y are perpendicular vectors.

    Recall that for any vector z:

    |z|^2 = z * z

    So what should |x + y|^2 and |x - y|^2 be?
     
  6. Sep 18, 2003 #5
    Thanks man
     
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