Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Set Theory

  1. Jun 14, 2016 #1
    Can some please explain to me how to solve these two questions?
    Let A, B and C be any sets, prove that:
    (a) A-B ⊂ A
    (b) (A∩B) complement = A complement ∪ B and (A∪B) complement = A complement∩ B complement.
     
  2. jcsd
  3. Jun 14, 2016 #2

    Math_QED

    User Avatar
    Homework Helper

    We usually write out A\B instead of A -B

    Anyway, start to write down the definitions and see where you get.

    A\B = {x|x ∈ A and x ∉ B}
     
  4. Jun 14, 2016 #3
    Thank you very much for the correction.
    Well.... there are no definitions, it just says let A, B and C be any set, prove that A\B⊂A.
     
  5. Jun 14, 2016 #4

    Math_QED

    User Avatar
    Homework Helper

    Well, look up the definitions! How can you prove something without knowing what the definitions are?
     
  6. Jun 14, 2016 #5
    No definitions bro, just have to use x to prove it... That's why i'm confused.
     
  7. Jun 14, 2016 #6

    PeroK

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    He's talking about the definition of "subset"! As in, what does ##A-B \subset A## actually mean? You can't prove it unless you know what it means.
     
  8. Jun 14, 2016 #7
    oh... okay basically what it means is that all elements of A\B are contained inside A.
     
  9. Jun 14, 2016 #8

    PeroK

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Yes, although more simply and consistently you could say it means:

    Each element of A\B is an element of A.
     
  10. Jun 14, 2016 #9
    Yes, thank you very much sir.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Set Theory
  1. Set Theory (Replies: 1)

  2. Set Theory? (Replies: 2)

  3. Set theory issue (Replies: 1)

Loading...