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Homework Help: Assuming that the system (s,*) has an identity element ,prove that:

  1. Nov 2, 2012 #1
    assuming that the system (s,*) has an identity element. if the equation
    (a*b)*(c*d)=(a*c)*(b*d) holds for all a,b,c,d belongs to S ,

    ,prove that:* is associative and commutative .

    I tried so much but with no good result !

    any ideas ?
  2. jcsd
  3. Nov 2, 2012 #2


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    Homework Helper

    Hi Maths Lover! :smile:

    Try "commutative" first …

    put two of a b c or d equal to the identity. :wink:
  4. Nov 2, 2012 #3


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    What happens if you take c and d equal to the identity?
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