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Homework Help: Simple notation question

  1. Sep 15, 2007 #1
    I haven't done mathematics in a while and I have this question to do.

    Describe the following subests of the plane:

    a. R x {1,2,4}
    b. ([0,1] U [2,3]) x[0,1]
    c. ([0,1] U [2,3]) x ([0,1]x[2,3])

    2. I'm actually unsure of the relevant equations used for this sort of problem.

    3. Basically I think the first one is the lines x=1, x=2, x=4, y=1, y=2, and y=4.
    But in the back of my mind I think it's either only the y or the x equations. If someone could help me visualize this properly I think this problem would be much easier. Thanks.
  2. jcsd
  3. Sep 15, 2007 #2


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    Staff Emeritus
    Science Advisor

    Well the first one is a set of points such that the x value is any real number, and the y value is one of {1,2,4}. So, the first value for y gives [itex]\{(x,y):x\in\mathbb{R}, y=1\}[/itex]. Can you identify this as one of the lines you suggest? Doing so for the other values of y will give you your solution.

    For the other questions, think in the same way.
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