# Tagged: Eisenstein polynomial

## Problem 399

Prove that the cubic polynomial $x^3-2$ is irreducible over the field $\Q(i)$.

## Problem 335

Consider the cubic polynomial $f(x)=x^3-x+1$ in $\Q[x]$.
Let $\alpha$ be any real root of $f(x)$.
Then prove that $\sqrt{2}$ can not be written as a linear combination of $1, \alpha, \alpha^2$ with coefficients in $\Q$.

## Problem 333

Let $R$ be an integral domain and let $S=R[t]$ be the polynomial ring in $t$ over $R$. Let $n$ be a positive integer.

Prove that the polynomial
$f(x)=x^n-t$ in the ring $S[x]$ is irreducible in $S[x]$.

## Problem 234

Show that the polynomial
$f(x)=x^4-2x-1$ is irreducible over the field of rational numbers $\Q$.

## Problem 231

Show that $\Q(\sqrt{2+\sqrt{2}})$ is a cyclic quartic field, that is, it is a Galois extension of degree $4$ with cyclic Galois group.

## Problem 179

Prove that $\sqrt[m]{2}$ is an irrational number for any integer $m \geq 2$.

## Problem 89

Prove that the polynomial $x^p-2$ for a prime number $p$ is irreducible over the field $\Q(\zeta_p)$, where $\zeta_p$ is a primitive $p$th root of unity.

## Problem 82

Show that the polynomial $x^3-\sqrt{2}$ is irreducible over the field $\Q(\sqrt{2})$.