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Homework Help: Help absolute value proof?

  1. Oct 20, 2012 #1
    1. The problem statement, all variables and given/known data
    we know that |a| < c and |bl < c
    prove that : (la+bl + la-bl)/2 < c

    3. The attempt at a solution
    all i've gotten to so far is this : la+bl < 2c
    lal + lbl < 2c
    we have : la+bl < lal+lbl
    then la+bl < 2c
    i need to prove that la-bl < 0.?
    also by squaring all i gotten so far is (la+bl + la-bl)/2 < 2c...
  2. jcsd
  3. Oct 20, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi Andrax! :smile:
    If they're complex, it's not true.

    If they're real, then just try the 4 different ± possiblities, :wink:
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