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Math Help - Subring w/o identity

  1. #1
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    Subring w/o identity

    We need to verify if this is a subring with or without identity of M(R). The book says it is without identity, but I am confused.

    It is:

    all 2x2 matrices of the form (0 r; 0 0) for r rational.

    I don't see how this doesn't have identity since (0 r; 0 0)* (1 0; 0 1)=(0 r; 0 0)

    Thanks.
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  2. #2
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    Quote Originally Posted by zhupolongjoe View Post
    We need to verify if this is a subring with or without identity of M(R). The book says it is without identity, but I am confused.

    It is:

    all 2x2 matrices of the form (0 r; 0 0) for r rational.

    I don't see how this doesn't have identity since (0 r; 0 0)* (1 0; 0 1)=(0 r; 0 0)

    Thanks.
    Well, (1 0;0 1) does not have the form (0 r;0 0).
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  3. #3
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    Nevermind, I got it.....
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