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Math Help - subsets/open sets

  1. #1
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    subsets/open sets

    For any set S a subset of R, let S^o denote the union of all the open sets contained in S
    A) prove that S^o is an open set
    B) prove that S^o is the largest open set contained in S. That is, show that S^o a subset of S, and if U is any open set contained in S, then U a subset of S^o
    C) prove that S^o = int S
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  2. #2
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    Quote Originally Posted by luckyc1423 View Post
    For any set S a subset of R, let S^o denote the union of all the open sets contained in S
    A) prove that S^o is an open set
    B) prove that S^o is the largest open set contained in S. That is, show that S^o a subset of S, and if U is any open set contained in S, then U a subset of S^o
    C) prove that S^o = int S
    No sure what definition of ‘open’ you are using. This one is standard: A set S is open iff for each x is S there is a open set O_x which contains x and is a subset of S.

    Do you see how part A) results directly from that definition.

    For part B), any open set of S is a subset of S^o.

    For part C), a point t is in int(S) iff there is a open set O_t which contains t and is a subset of S.
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