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    hi guys, got this question cant realy do any of it duno where to start realy, if you know of a site that could help and send me in the right directiont that would be much appreciate, of if u know urself that would be even better thanks guys

    Sketch the following subsets of C, paying careful attention to whether
    or not the boundaries are included. Discuss whether each is open,
    closed or neither.
    a) A = {z E C | 1 < |z -2i|j < 2}
    b) R
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    What are your definitions of 'open' and 'closed'? I'm not sure what you mean by the "j" in your first question, and indeed you might find it easier to try b) before a).
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    For part a, don't you just draw a circle with radius 1, with 2i as the centre? Then draw another, same centre but radius 2. Then shade everything thats outside the smaller circle but inside the larger circle

    As far as I'm aware, Open is where you include everything (except the end points). and Closed is where you include everything within the interval (including the end points)

    You can tell the bounderies aren't included since its less than not less than or equal to
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    (Original post by Weeman5872)

    As far as I'm aware, Open is where you include everything (except the end points). and Closed is where you include everything within the interval (including the end points)
    That's my understanding too.

    When you're sketching, the convention is that you use a dashed line to indicate an open set - associated with a strong inequality, and a solid line means a closed set (includes its end-points) which comes from a weak inequality
 
 
 
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