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Thread: Is it a function?

  1. #1
    Junior Member
    Sep 2008

    Is it a function?

    Set A contains zip codes from the US and set B contains US citizen's social security numbers. The elements of these sets can be paired in that each person has a zip code for their legal address (or domicile) and each person has a social security number.

    (a) If these are written as orderes pairs of the form (Zip code, Social security number) do we have a function? why or why not?

    (b) Social security number, zip code? why or why not?

    for (a) i said yes because if it was to be plotted it would past the line test.

    for (b) i said no because it would not pass the line test.

    Does the line test have anything to do with it? Am I right? What did I do wrong?

    Hint: Evey US citizen has exactly one legal address even if they own more than 1 house or live part time in one town and part time in another town (like a college student living in a door). Determining which address is your legal address can be quite tricky for some people, but it is important for tax purposes.
    Last edited by asweet1; Sep 3rd 2009 at 06:37 AM.
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  2. #2
    MHF Contributor Calculus26's Avatar
    Mar 2009
    A function is defined so that for each input x there is a single ouput y

    in the ordered pair(x,y)

    For each zip code there are many social security #s so a is not a function

    However for each social security # there is only one zip code so b is a function.

    The vertical line test would apply if you were willing to plot
    all (zipcode,social security ) pairs but that would seem unreeasonable
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