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Sum of three cosines equals 1

  1. Feb 29, 2012 #1
  2. jcsd
  3. Feb 29, 2012 #2
    If OP=d, the coordinates of P are (cos α1,cos α2,cos α3)d. Now, express the length of OP using Pythagoras and you get the desired relation.
  4. Mar 1, 2012 #3
    Got it! Thanks!
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