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

Help with Set questions please

  1. Jan 18, 2012 #1
    1. The problem statement, all variables and given/known data

    Hi, I need help with a couple of Set questions I just can't get my head around.

    The question starts with:


    A = (-1, -2, 1, 2, 3, 5)

    List the members of the following sets:

    i) (x [itex]\in[/itex] R: x = m/n for m, n [itex]\in[/itex] A)

    ii) (x [itex]\in[/itex] Z: x = m/n for m, n [itex]\in[/itex] A)

    2. Relevant equations

    3. The attempt at a solution

    R will be real numbers and Z will be integers? I just can't seem to understand the rest. Any help ould be greatly appreciated.

  2. jcsd
  3. Jan 18, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    For i:

    Generate all of the fractions you can make from the elements of set A, but using one element for the numerator and one element (possibly the same element) the denominator.

    For ii:

    Do the same as for part i, except you keep only the fractions which simplify to be integers.
  4. Jan 18, 2012 #3
    Thanks for your response!

    So for i)

    I use A = (-1, -2, 1, 2, 3, 5) and make fractions, every possible combination?

    -1/-2 = a half 1/2, but I wouldn't list that as it is not in set A?

    so next would be -1/1 which is -1, so that is in set A?

    I still don't get it I think.
  5. Jan 18, 2012 #4


    User Avatar
    Science Advisor

    No, the results don't have to be in A! You need to form all possible fractions- as the problem said, m/n with both m and n from A. All of those will be in (i) but only those that reduce to integers will be in (ii).
  6. Jan 18, 2012 #5
    Ahh ok thank you HallsofIvy!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook