# Questions tagged [polynomial-rings]

This tag is used for questions on polynomials rings in an arbitrary number of variables related to different topics studied in ring theory and commutative algebra. Questions related to high-school polynomials level or similar should use the tag "polynomials".

135 questions
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### How to deal with polynomial quotient rings

The question is quite general and looks to explore the properties of quotient rings of the form $$\mathbb{Z}_{m}[X] / (f(x)) \quad \text{and} \quad \mathbb{R}[X]/(f(x))$$ where $m \in \mathbb{N}$ ...
2answers
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### Subrings $A$ of $\mathbb{F}_p[x]$ such that $\dim_{\mathbb{F}_p}\mathbb{F}_p[x]/A=1$.

Suppose we have the ring $\mathbb{F}_p[x]$ of polynomials with coefficients in the Galois field with $p$ prime number elements. I want to find all subrings $A$ containing the identity such that when ...
3answers
438 views

### Show that the ideal generated by two polynomials is actually equivalent to the ideal generated by a single polynomial

I've been asked to show that the ideal $I = \langle x^3 - 1, x^2 - 4x + 3\rangle$ in $\mathbb{C}[x]$ is equivalent to $I = \langle p(x)\rangle$ for some polynomial $p(x)$. Now, I'm not quite sure ...
2answers
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### $\Bbb R[X,Y]/(F) \cong \Bbb R[Z]$ and $F_X G_Y - G_X F_Y \in \Bbb R^*$

Hope this isn't a duplicate. I was trying to solve the following problem : Let $F,G \in \Bbb R[X,Y]$ satisfy $\Bbb R[F,G]= \Bbb R[X,Y]$. Prove that : (i) $\Bbb R[X,Y]/(F) \cong \Bbb R[Z]$ , for ...
1answer
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### Show the following polynomial is Irreducible over the given ring

Studying for a qualifying exam and this practice problem flat out has me stumped. I wish to show that the polynomial $(y+8)^2x^3 - x^2 + (y+7)(y+8) - y - 12$ is irreducible over $\mathbb{Q}[x, y]$. ...
1answer
117 views

### Factoring $x^n + 1$.

By the Fundamental Theorem of Algebra, every polynomial of degree $n$ can be factored into a product of $n$ linear polynomials. As an example, since the polynomial $x^5 +1$ has the five complex ...
3answers
198 views

### How do we know that automorphisms on polynomials have a polynomial like form?

Let $F$ be a field and $\sigma:F[x]\to F[x]$ be automorphism, $\sigma(a) = a$ for all $a\in F$. I'm supposed to show that $\sigma(f(x)) = f(ax+b)$ for some $a\not = 0$ and $b$ in $F$. Now I've got a ...
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### Counting irreducible polynomials over finite fields [duplicate]

How many irreducible polynomials in $Z_2[x]$ of degree $3$? I have discussed this with my friend before and we found that $x^3 + x^2 + 1$ and $x^3+x+1$ are the two said polynomials which irreducible....
2answers
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### Show that $\mathbb{Z}_5[x]/(x^2+x+1)\cong\mathbb{Z}_5[x]/(x^2+x+2)$

I think this problem is from Gallian, prof couldn't solve it. Notice that both polynomials have no roots. I tried to construct an onto homomorphism $\varphi:\mathbb{Z}_5[x]\to\mathbb{Z}_5/(x^2+x+2)$ ...
1answer
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### Why isn't this criterion for determining irreducibilty working?

I have learned this criterion for irreducibility of polynomials: Let $R$ be an integral domain, let $I$ be a proper ideal of $R$, and let $p(x)$ be a non-constant monic polynomial in $R[x]$. If the ...
2answers
365 views

### Ideal of a Polynomial ring $R$ which is not principal.

Let $R$ be the ring given by $R=\mathbb Z+x\mathbb Q[x]$. Then show that: 1) $R$ is an integral domain and its units are $+1$ and $-1$. 2) $x$ is not prime in $R$ and describe the quotient ...
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