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Math Help - Help with proving a function is not onto.

  1. #1
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    Help with proving a function is not onto.

    Suppose that f:A->B and g:B->C. Prove that if f is not onto and g is one-to-one, then gof is not onto.

    Am I right in saying that we need to find some x in B which shows that f is not onto? Then we can say that for any a in A, gof(a) does not equal g(x)? I don't know where to go from here or even if "here" is a starting point.

    Thanks for any help!

    Also, how do you use LaTeX in this forum? I've seen it used in other posts but I can't figure out how to do it.
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  2. #2
    Super Member
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    Athens, OH, USA
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    Re: Help with proving a function is not onto.

    Hi,
    To use Latex, see the forum Latex Help. For this specific function problem, see the attachment:

    Help with proving a function is not onto.-mhfdiscretemath1.png
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