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Math Help - Question on which set to use in showing something is a group

  1. #1
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    Question on which set to use in showing something is a group

    Hi guys, I just have some questions on this problem regarding some details, any clarification would be greatly appreciated!



    Cheers!
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  2. #2
    Senior Member abhishekkgp's Avatar
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    Quote Originally Posted by usagi_killer View Post
    Hi guys, I just have some questions on this problem regarding some details, any clarification would be greatly appreciated!



    Cheers!
    if we are set out to see whether <R,*> is a group or not then a*0 remains undefined since '*' was defines only on R\{0} . so one can't be sure that <R,*> is a binary structure to begin with. So i would say that one can't conclude that <R,*> is a group if have * as defined in the question.
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  3. #3
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    the author of the book should be publicly flogged for posing such an ill-formed question.

    as posed, <R,*> is not a group, because * has not been defined on all of R. but this is probably not the question the author meant to pose.

    he probably meant to ask if <R-{0},*> was a group.
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  4. #4
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    thanks for that!

    I thought it might've been a typo as well... i will email my lecturer who set this question
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  5. #5
    MHF Contributor Swlabr's Avatar
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    Quote Originally Posted by usagi_killer View Post
    Hi guys, I just have some questions on this problem regarding some details, any clarification would be greatly appreciated!



    Cheers!
    You say e/|e| is the identity element since x cannot be 0 and thus e is defined...however, it is not defined uniquely. An identity element is always unique (if, say, x and y are identity elements then xy=x and xy=y, so x=y), so something is amiss.

    Remember that e is a real number, so try and place it on the number line. e=...? This will help you to see what is amiss...
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