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Math Help - just a few simple questions on set

  1. #1
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    just a few simple questions on set

    Let S={1,2,3}. Then ⊆ S. Why is this true?

    ⊆{}. Why is this true?

    The set {x∈ : 2x2 - 7x- 4 =0}. How come this one has 2 elements instead of 1?

    Thanks.
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  2. #2
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    Re: just a few simple questions on set

    Quote Originally Posted by naturebuilder View Post
    Let S={1,2,3}. Then ⊆ S. Why is this true?
    ⊆{}. Why is this true?
    The statement that A\subseteq B means that \text{if }x\in A\text{ then }x\in B~.
    So for any set X it is true that \emptyset\subseteq X
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