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Confused with domain

  1. Oct 8, 2008 #1
    I just have a question which I'm confused about,

    this is the same right?

    Domain is (-∞,0) U (0,+∞)

    and

    Domain D: {XER, x ≠ 0}



    and this is the same right?

    Domain is (-∞,0) U (5,+∞)

    and

    Domain D: {XER, x ≠ 0, x≠ 5}



    Attempt :

    I know that U is used to connect functions,

    I'm asking this here since I couldn't find notation online
     
  2. jcsd
  3. Oct 8, 2008 #2

    Dick

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    U means union. You are right on the first one. Not so good for the second one. D is the set of xER, where x is not an element of [0,5], the closed interval between 0 and 5.
     
  4. Oct 8, 2008 #3
    (-∞,0) u [0,5] u (5,+∞) ?

    do I always have to include for example the [0,5] when function is XER?

    thanks
     
  5. Oct 8, 2008 #4

    Dick

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    That's all of the reals. The set you are describing in the second part is the set of all real x (xER) SUCH THAT x<0 OR x>5. It has two pieces. The xER doesn't say you are including all reals, it just says you are considering ONLY reals.
     
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