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Triangle innequality proof question

  1. Nov 23, 2008 #1
    for "a" and "b" are real numbers prove that:


    i need to use the triangle innequality
    |a|-|b|=< |a+b| <= |a| + |b|

    how to apply it to my question?
    it a long way from
    triangle innequality formula to the expression that i was given in the question

  2. jcsd
  3. Nov 23, 2008 #2
    The triangle inequality reads


    for any two vectors x,y

    Take in particular

    x=a-b, y=b


    x=b-a, y=a

    What do you get?
    Then use, |a-b|=|b-a| and the fact that if |a-b| is greater than c and greater then -c, it must be greater than |c|. (What is c?)
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