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Question about ideal of a ring

  1. Mar 12, 2011 #1
    Hello Experts,

    Again a Q and what I did, please tell me what I am doing wrong:

    Given that there is a ring of matrices above Z (integers) Mn(Z) and 2 ideals I, J of this ring.

    I need to prove that they are commutative: IJ = JI

    What I did is that:

    For all i in I and for all M in Mn(Z) n is the the size of a matrix n x n

    M*i in I and i*M is also in I.

    same with J : j*M in J and M*j is in J

    For every k in J and for every h in I:

    kh = j*M*i*M = j*(M*i)*M = .... I don't know what to do from here.... please guide me.
  2. jcsd
  3. Mar 16, 2011 #2
    Hey Duke!
    I suggest you to check again your hypothesys instead.
    Well, [tex]\mathbb{Z}[/tex] is a ring with unity, right? What's the form of it's ideals? What's the form of the ideals of [tex]M_{n}(\mathbb{Z})[/tex]?

    The problem of your approach is that I can't really see a way to use your hypothesys.
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