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Homework Help: Help with basic notation

  1. Sep 23, 2012 #1


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    1. The problem statement, all variables and given/known data

    In an intro Economics course, the teacher gave us some questions regarding function notation. I learned calculus to a decent level, but I have problems with notation.

    2. Relevant equations

    Question 1. Give an explicit expression for the following set: { x : x ∈ Z and x < 2 }
    Question 2. Give an example of an element (y) of the following set: Y = Y1 x Y2 x Y3 , whereY1 = set of train engines = { green, blue, red }, Y2 =set of train cars = { passenger, boxcar, tanker }, Y3 = set of cabooses = { red }.
    Question 3. Consider the function f : X → Y, when Y = R and f and X are defined as
    follows: X = {(1,1,0), (1,0,1), (1,0,0), (0,1,0), (0,0,1)} and f (x) = x1 + x2 + 2x3. Now what is the set { x : f (x) = 2, x ∈ X }? (NOTE: It is not x*2 or 2x*3, but x with a little two beside it, 2x with a little three beside it).

    3. The attempt at a solution

    Question 1: I don't get what "explicit expression" means. It wants an integer less than two...
    {x: (- infinity, 2), x ∈ Z}
    Question 2: [Green, boxcar, red caboose]
    Question 3: (1, 1, 0)

    Can someone please tell me where/if I went wrong?
    Last edited: Sep 23, 2012
  2. jcsd
  3. Sep 24, 2012 #2


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    Science Advisor
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    Those little numbers are called subscripts. You can use the X2 icon to make subscripts. Apparently they are labelling the members of X like x1=(1,1,0), x2= (1,0,1), etc, using the subscripts as indices to label them.
    It might mean {1,0,-1,-2,-3,...} where the ... means continue.
    Usual notation would use ( ) instead of [ ].
    Add x1, x2 and 2x3 in the usual way.
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