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Math Help - A union B union C

  1. #1
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    A union B union C

    I need the formula to get the union of A,B,C. For Example. You have set A, set B and Set C. You have all of the information provided to you, other than what the union of all three is.

    I have this formula(since i dont know how to input math symbols. int. means intersection):

    aUbUc = (a + b + c) - (a int c) - (a int b) - (b int c) + (a int b int c)

    would that formula work?
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  2. #2
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    If we use \left| A \right| to stand for the number of elements is set A then
    \left| {A \cup B \cup C} \right| = \left| A \right| + \left| B \right| + \left| C \right| - \left| {A \cap B} \right| - \left| {B \cap C} \right| - \left| {A \cap C} \right| + \left| {A \cap B \cap C} \right|.
    That is called the inclusion-exclusion principle.
    Do a web search on that topic. There are many generalizations of that idea.
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