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Real Analysis ( measure theory)

  1. Aug 28, 2010 #1
    1. The problem statement, all variables and given/known data
    Let A and B be bounded sets for which there is [tex]\alpha[/tex] > 0 such that |a -b| [tex]\geq[/tex][tex]\alpha[/tex]
    for all a in A and b in B. Prove that outer measure of ( A [tex]\bigcup[/tex] B ) = outer measure of (A) + outer measure of (B)

    2. Relevant equations

    We know that outer measure of the union is less than the addition of outer measure of the single sets
    we need to show that it is greater than the addition of outer measures of the sets

    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Aug 28, 2010 #2

    Office_Shredder

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    Have you tried anything? The fact that the two sets have a gap between them is obviously important. Try going straight to the definition of outer measure and see if you can spot anything useful
     
  4. Aug 29, 2010 #3
    I know that they are disjoint but it is not clear for me how to use this in proving that
    the outer measure of union is greater than the addition of the ouetr measure of the sets.

    but I tried this:

    A [tex]\bigcup[/tex]B[tex]\subset[/tex] O for some set O covering A and B
    i.e A [tex]\bigcup[/tex]B[tex]\subset[/tex]([tex]\bigcup[/tex] I[tex]\cup[/tex]J)
    So m(A[tex]\bigcup[/tex]B)< m(A) + m(B)
    or m(A[tex]\bigcup[/tex]B) + [tex]\epsilon[/tex] > m(A) + m(B)
    and since [tex]\epsilon[/tex] is arbirary. then it is done.

    but I think there is a gab in this proof and I don't know why
     
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