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Triangle inequality, parallelogram equality

  1. Feb 17, 2006 #1
    what does a triangle have to do with triangle inequality, and what does a paralllelogram have to do with parallelogram equality?
  2. jcsd
  3. Feb 17, 2006 #2


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  4. Feb 17, 2006 #3
    i'm still confused:
    "triangle inequality is the theorem stating that for any triangle, the measure of a given side must be less than the sum of the other two sides but greater than the difference between the two sides."
    yet "|x+y| ≤ |x|+|y| " shouldn't mean "|z|≤ |x|+|y| "?
  5. Feb 17, 2006 #4
    If you think of x and y as vectors in space they will form a triangle with a third vector that is the vector sum x+y so the inequality makes sense.
  6. Feb 18, 2006 #5
    thank you very much!!!
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