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Homework Help: In each part specify the set by listing its elements

  1. Jan 2, 2007 #1
    Can anyone offer any help with these questions?

    Question 1:

    In each part specify the set by listing its elements:

    { x | x Є Z and (x+1)² < 10 }

    Answer:

    am i supposed to write out all the possible x's, so that my answer would be:

    {0,1,2,-1,-2,-3,-4}

    or do i write out the over all set which is:

    {0,1,4,9}

    Question 2:

    If A={1,2,3,4,5}, which of the following sets equal A?

    f) { x | x Є N and x < 6}

    Answer:

    i put that f) doesn't equal A because 0 belongs to N but doesn't belong to A...is that right?

    Question 3:

    Use Venn diagrams to show that for sets X, Y:

    a) X(X+Y) = X
    b) X + XY = X
    c) X – Y = XY’

    Answer:

    i don't know what to do
     
  2. jcsd
  3. Jan 2, 2007 #2

    radou

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    Homework Helper

    You did it right. You wrote down the set of all 'x-es' which satisfy the given conditions.

    You have to consult your textbook for that one. Suprisingly enough, some authors consider 0 to be a natural number, and some don't. Although the most I've read say that 0 is not in N.

    '+' is an operation which doesn't apply for sets. Perhaps you ment the union? Or is it just notation?
     
  4. Jan 2, 2007 #3
    Thanx for the help with question 1

    For Question 2, that's why i'm confused because i thought that 0 belonged to N...but in our notes my teacher didn't say it did; i think i'll leave it like that!

    For Question 3, i copied and pasted the question there are about 4 questions like that, and i just don't understand what to do...maybe the + does mean union... but do you think that - means intersecton?
     
  5. Jan 2, 2007 #4

    radou

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    Yes, follow your teacher's notes.

    '-' means the set difference, I saw this notation in a book once. If you know what Venn diagrams are (google it up if you don't), you shouldn't have any problems.

    But, I don't understand what, for example, XY represents?
     
  6. Jan 2, 2007 #5
    i know what venn diagrams are, maybe XY means X intersection Y...no?
     
  7. Jan 2, 2007 #6

    radou

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    Could be. If so, you'll answer your question easily.
     
  8. Jan 2, 2007 #7
    The statement X(X+Y) = X is true if '+' denotes intersection, and that invisible operation, that could possibly confuse someone to believe that the sets are being "multiplied," denotes union.
     
  9. Jan 2, 2007 #8

    radou

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    It is true if '+' denotes union and ' ' denotes intersection, too. :smile:
     
  10. Jan 2, 2007 #9
    Thank you radou and neutrino!
     
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