Show that the rings Z[x] and Z are not isomorphic

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SUMMARY

The rings Z[x] and Z are not isomorphic due to fundamental structural differences. While it is established that the quotient ring Z[x]/(x) is isomorphic to Z, Z[x] itself is not a Principal Ideal Domain (PID), which Z is. The existence of ideals such as I = ⟨2, 1+x⟩ in Z[x] demonstrates that not all ideals can be generated by a single element, a property that Z possesses. Therefore, the non-isomorphism is confirmed through the analysis of their ideal structures.

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  • Understanding of ring theory, specifically the definitions of rings and ideals.
  • Familiarity with Principal Ideal Domains (PIDs) and their properties.
  • Knowledge of quotient rings and their isomorphism properties.
  • Basic concepts of polynomial rings, particularly Z[x].
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  • Study the properties of Principal Ideal Domains (PIDs) in depth.
  • Learn about the structure and properties of polynomial rings, specifically Z[x].
  • Explore the concept of ideals in ring theory, focusing on examples of non-PIDs.
  • Investigate quotient rings and their applications in proving isomorphisms.
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Mathematicians, algebra students, and anyone studying abstract algebra, particularly those interested in ring theory and the properties of polynomial rings.

Mr Davis 97
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Homework Statement


Show that the rings Z[x] and Z are not isomorphic

Homework Equations

The Attempt at a Solution


I want to show that these are not isomorphic. The thing is that I already know that ##\mathbb{Z}/(x) \cong \mathbb{Z}##, but for some reason I can't find specific structural properties of ##\mathbb{Z}[x]## that are different than ##\mathbb{Z}##
 
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##\mathbb{Z}/(x) \cong \mathbb{Z}##?
 
fresh_42 said:
##\mathbb{Z}/(x) \cong \mathbb{Z}##?
I meant to write ##\mathbb{Z}[x]/(x) \cong \mathbb{Z}##
 
What if you assumed an isomorphsm ##\varphi\, : \,\mathbb{Z}[x] \longrightarrow \mathbb{Z}##. Then ##\varphi((x)) ## is an ideal in ##\mathbb{Z}##, say ##\varphi((x)) = n\mathbb{Z}## with ##\varphi(x)=n##. What do you get if you factor this ideal on both sides?
 
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Mr Davis 97 said:

Homework Statement


Show that the rings Z[x] and Z are not isomorphic

Homework Equations

The Attempt at a Solution


I want to show that these are not isomorphic. The thing is that I already know that ##\mathbb{Z}/(x) \cong \mathbb{Z}##, but for some reason I can't find specific structural properties of ##\mathbb{Z}[x]## that are different than ##\mathbb{Z}##
Another idea is to use the fact that ##\mathbb{Z}[x]## is no PID, e.g. ##I:=\langle 2, 1+x \rangle##.
 
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