Recent content by julia89

  1. J

    Prove or Disprove: Closure of Int(X)=X

    Prove or disprove Closure of the Interior of a closed set X is equal to X so clos(intX)=X I think it is true, but i don't know how to prove it I thought that clos(int(X))=int(X)+bdy(int(X))=X thanks, julia
  2. J

    Set of Integers: Open or Closed?

    ow sorry I switched open and closed I meant that it was a closed set and not open
  3. J

    Set of Integers: Open or Closed?

    Homework Statement is the set of integers open or closed Homework Equations The Attempt at a Solution I thought not closed open because R/Z=Union of open intervals like ...U(-1,0)U(0,1)U...
  4. J

    Calculating Diameters of Interval Unions

    so if i am right 1. Diam of (-1,1]U(2,3)=2+1=3 2.Diam of (1,1/2)U(1/4,1/8)U(1/16,1/32)U...=1/2+1/4+1/16+... Is this correct?
  5. J

    Calculating Diameters of Interval Unions

    I know that the diameter for an interval [a,b] is defined as b-a but what is 1. Diam of (-1,1]U(2,3) 2.Diam of (1,1/2)U(1/4,1/8)U(1/16,1/32)U... Thanks
  6. J

    Find a set A (subset of R,set of real numbers) and an element a of R

    Find a set A (subset of R,set of real numbers) and an element a of R such that there is no bijecton from a+A(we add a to the set A)to A. I can't find a good example. Can someone help Are we done if we choose the empty set? (And is the empty set a subset of R?) Thank you