Rings Isomorphism: Proving R & R_2 Subrings of Z & M_2(Z)

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Homework Help Overview

The discussion revolves around proving that the set R, defined as a+b√2 where a and b are integers, is a subring of the integers Z, and that R₂, consisting of specific 2x2 matrices, is a subring of M₂(Z). Participants are also tasked with demonstrating that the mapping from R to R₂ is an isomorphism.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the requirements for proving closure under addition and multiplication, as well as the presence of identity elements in R and R₂. Questions arise about the specific forms of elements in R and how to express sums of these elements. There is also inquiry into the axioms needed to establish subring properties and theorems that might simplify the proof process.

Discussion Status

Some participants express confusion about the definitions and properties needed to prove the subring status, while others seek clarification on the steps involved in the proof. Guidance has been offered regarding the necessary axioms and theorems that may reduce the workload in proving the subring properties.

Contextual Notes

Participants mention the need to show closure under addition and multiplication, as well as the inclusion of identity elements, while also questioning the implications of √2 not being an integer. There is a recognition of the complexity of the task for those new to the topic.

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3. Let R = a+b \sqrt{2} , a,b is integer and let R_{2} consist of all 2 x 2
matrices of the form [\begin{array}{cc} a & 2b \\ b & a \\ \end{array} }]

Show that R is a subring of Z(integer) and R_{2} is a subring of M_{2} (Z). Also. Prove that the mapping from R to R_{2} is a isomorphism.
 
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Hi, what did you try already and where are you stuck? Then we'll know how to help you!
 
I am lost totally in this question. I know i need to do this.
need to show it is closed under addition, multiplication containing identity to prove it is a subring and show that it is surjective and injective. to show that it is isomorphism.

Can you help me out in this question?
 
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So, closed under addition/multiplication, what does that mean?? How would you show this?
 
that the part i am struck with. a+b\sqrt{2} + c+d\sqrt{2} ? but \sqrt{2} not an integer
 
dreamer.ande said:
that the part i am struck with. a+b\sqrt{2} + c+d\sqrt{2} ? but \sqrt{2} not an integer

You will want to write a+b\sqrt{2}+c+d\sqrt{2} in the form e+f\sqrt{2}, since by definition, elements in R have this form.

We are not claiming that \sqrt{2} is an integer!
 
how many axiom do i need to show to prove that it is a subring of a ring?
There are five axiom to show?
How to show that first axiom : containment. R belong to Z?

Can you show me the proper step of proving in such question as I always have problem in such question?
 
Last edited:
dreamer.ande said:
how many axiom do i need to show to prove that it is a subring of a ring?

Normally all of them. But luckily you have theorems that limit the amount of work you need to do.

A certain theorem tells you that you only need to show that R is closed under addition and multiplication, that 0 and 1 are in R, and that -a is in R for every a.

So you only need to show 5 things. However, if you did not see such a theorem, then you will need to show all the axioms!
 
Could you show me how to do it for the first part and I try out the second part?
Sorry, I am new to this thing. Very Confusing for me.
 

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