Discrete Math question

This is a discussion on Discrete Math question within the Tech Board forums, part of the Community Boards category; Hey all, I'm very sorry that this is off topic, but I couldnt find anywhere else to ask this type ...

  1. #1
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    Discrete Math question

    Hey all,

    I'm very sorry that this is off topic, but I couldnt find anywhere else to ask this type of question on the web.

    Does anyone know of a GOOD message board for discrete structures/discrete math?

    Anyways, I mine as well as the question.

    A function g is defined as g(A) = T U (A /\ S) where T, S are fixed subsets of universe U . Does g have an inverse? If so, what is it. If not, why not?

    ( /\ is intersection operator )

    Thank you all and sorry again for the off topic post!!

    Justin

  2. #2
    5|-|1+|-|34|) ober's Avatar
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    Link to FD's Math Forum

    3 years ago, I could have done that problem for you, but I barely got out of that class and I sure don't remember much from it. I think that was one of the most confusing classes I ever took in college.

  3. #3
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    g(A) = T U (A /\ S)
    This is invertible only if g(A) is one-to-one and unto.

    I was thinking if we can prove the inverse may not exist by counter-example:

    Let say
    U = {1,2,3,4,5,6,7,8,9,10,11,12}
    T = {1,2,3,4}
    A = {5,6,7,8}
    S = {9,10,11,12}

    g(5) = {1,2,3,4} // since 5 /\ S is an empty set
    = T

    g(6) = {1,2,3,4} // for same reasons
    = T

    5!=6 but g(5) = g(6), therefore it may not be one to one.

    Correct if i am wrong.

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