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Indigo5684
2025-09-30 13:19:29 -05:00
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commit 78c6ed9889
8 changed files with 29 additions and 29 deletions

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@@ -36,9 +36,9 @@ $$
where either $\deg r(x) < \deg g(x)$ or $r(x)$ is the zero polynomial.
**Collary**. Let $F$ be a field. Then, an element $\alpha \in F$ is a zero of $p(x) \ in F[x]$ if and only if $(x-\alpha)$ is a factor of $p(x)$.
**Corollary**. Let $F$ be a field. Then, an element $\alpha \in F$ is a zero of $p(x) \ in F[x]$ if and only if $(x-\alpha)$ is a factor of $p(x)$.
**Collary**. Let $F$ be a field. Then, a nonzero polynomial $p(x) \in F[x]$ with degree $n$ can have at most $n$ distinct zeros in $F$.
**Corollary**. Let $F$ be a field. Then, a nonzero polynomial $p(x) \in F[x]$ with degree $n$ can have at most $n$ distinct zeros in $F$.
**Definition**. A monic polynomial $d(x)$ is the *greatest common divisor* of polynomials $p(x), q(x) \in F[x]$ if $d(x)$ evenly divides both $p(x)$ and $q(x)$. We write $\gcd(p(x), q(x)) = d(x)$. This polynomial is unique.
@@ -52,7 +52,7 @@ where either $\deg r(x) < \deg g(x)$ or $r(x)$ is the zero polynomial.
**Lemma**. Gauss's Lemma. Let $p(x) \in \mathbb{Z}[x]$ be monic such that $p(x)$ factors into two polynomials $\alpha(x), \beta{x} \in \mathbb{Q}[x]$, with the degrees of both strictly less than the degree of $p(x)$. Then, there exists two polynomials $a(x), b(x) \in \mathbb{Z}[x]$ such that $p(x) = a(x)b(x)$, and $\deg \alpha(x) = \deg a(x)$ and $\deg \beta(x) = \deg b(x)$.
**Collary**. Let $p(x) \in \mathbb{Z}[x]$ be monic with constant term $a_0$. Then, if $p(x)$ has a zero in $\mathbb{Q}$, then it also has a zero $\alpha$ in $\mathbb[Z]$. Furthermore, $\alpha$ divides $a_0$.
**Corollary**. Let $p(x) \in \mathbb{Z}[x]$ be monic with constant term $a_0$. Then, if $p(x)$ has a zero in $\mathbb{Q}$, then it also has a zero $\alpha$ in $\mathbb[Z]$. Furthermore, $\alpha$ divides $a_0$.
**Theorem**. Eisenstein's Criterion. Let $p$ be prime, and suppose that

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@@ -18,9 +18,9 @@ $$
Additionally, $F_D$ is unique. That is, given field $E$ such that $E \supset D$, there exists a map $\psi: F_D \rightarrow D$ giving an isomorphism such that $\psi(a) = a$ for all $a \in D$.
**Collary**. 18.6: Let $F$ be a field of charactaristic $0$. Then, $F$ contains a subfield isomorphic to $\mathbb{Q}$.
**Corollary**. 18.6: Let $F$ be a field of charactaristic $0$. Then, $F$ contains a subfield isomorphic to $\mathbb{Q}$.
**Collary**. 18.6: Let $F$ be a field of charactaristic $p$. Then, $F$ contains a subfield isomorphic to $\mathbb{Z}_p$.
**Corollary**. 18.6: Let $F$ be a field of charactaristic $p$. Then, $F$ contains a subfield isomorphic to $\mathbb{Z}_p$.
## Section 18.2 - Factorization in Integral Domains
@@ -49,7 +49,7 @@ Additionally, $F_D$ is unique. That is, given field $E$ such that $E \supset D$,
**Theorem**. 18.12: Let $D$ be a PID, and let $\langle p \rangle$ be a nonzero ideal in $D$. Thus, $\langle p \rangle$ is a maximal ideal if and only if $p$ is irreducible.
**Collary**. 18.13: Let $D$ be a PID. For any $p \in D$, if $p$ is irreducible, then $p$ is prime.
**Corollary**. 18.13: Let $D$ be a PID. For any $p \in D$, if $p$ is irreducible, then $p$ is prime.
**Lemma**. 18.14: Let $D$ be a PID. Let $I_1 \subseteq I_2 \subseteq \ldots$. Then, there exists some integer $N$ such that $I_n = I_N$ for all $n > N$. That is, any chain of ideals converges.
@@ -57,7 +57,7 @@ Additionally, $F_D$ is unique. That is, given field $E$ such that $E \supset D$,
**Theorem**. 18.15: Every PID is a UFD. Note that the converse is not true.
**Collary** 18.16: Let $F$ be a field. Then, $F[x]$ is a UFD.
**Corollary** 18.16: Let $F$ be a field. Then, $F[x]$ is a UFD.
---
@@ -74,7 +74,7 @@ Additionally, $F_D$ is unique. That is, given field $E$ such that $E \supset D$,
**Theorem**. 18.21: Every Euclidian domain is a PID.
**Collary**. Every Euclidian domain is a UFD.
**Corollary**. Every Euclidian domain is a UFD.
---
@@ -88,13 +88,13 @@ Additionally, $F_D$ is unique. That is, given field $E$ such that $E \supset D$,
As a direct consequence, we see the following.
**Collary**. Let $D$ be a UFD, and $F = F_D$. Then, a primitive polynomial $p(x) \in D[x]$ is irreducible in $D[x]$ if and only if it is irreducible in $F[x]$.
**Corollary**. Let $D$ be a UFD, and $F = F_D$. Then, a primitive polynomial $p(x) \in D[x]$ is irreducible in $D[x]$ if and only if it is irreducible in $F[x]$.
**Collary**. Let $D$ be a UDF, and $F = F_D$. Then, if a monic polynomial $p(x) \ in D[x]$ can be written as $p(x) = f(x)g(x)$ with $f(x), g(x) \in F_D[x]$, then $p(x)$ can be written as $p(x) = f_1(x)g_1(x)$, where $f_1(x), g_1(x) \in D[x]$.
**Corollary**. Let $D$ be a UDF, and $F = F_D$. Then, if a monic polynomial $p(x) \ in D[x]$ can be written as $p(x) = f(x)g(x)$ with $f(x), g(x) \in F_D[x]$, then $p(x)$ can be written as $p(x) = f_1(x)g_1(x)$, where $f_1(x), g_1(x) \in D[x]$.
**Theorem**. If $D$ is as UFD, then $D[x]$ is a UFD.
**Collary**. This theorem has several collaries:
**Corollary**. This theorem has several collaries:
1. Given a field $F$, since $F$ is a PID, it is also a UFD. Thus, $F[x]$ is a UFD.
2. The ring of polynomials over integers, $\mathbb{Z}[x]$ is a UFD.

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@@ -120,9 +120,9 @@ This direct product is in itself an $R$-module.
**Theorem**. For any set $A$, there is a free $R$-module $F(A)$ on $A$ such that $F(A)$ satisfies the universal property: if $M$ is any $R$-module, and $\varphi: A \rightarrow M$ is a map of sets, there eixts a unique $R$-module homomorphism: $\Phi: F(A) \rightarrow M$ such that $\Phi(a) = \varphi(a)$ for all $a \in A$.
**Collary**. If $F_1$ and $F_2$ are free modules on $A$, then there is a unique isomorphism between $F_1$ and $F_2$, which is the identity map on A.
**Corollary**. If $F_1$ and $F_2$ are free modules on $A$, then there is a unique isomorphism between $F_1$ and $F_2$, which is the identity map on A.
**Collary**. If $F$ is a free $R$-module with basis $A$, then $F \cong F(A)$.
**Corollary**. If $F$ is a free $R$-module with basis $A$, then $F \cong F(A)$.
**Definition** For a free module $F$ with basis $A$, if $R$ is commutative, tthen the *rank* of $F$ is the cardinality of $A$.

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@@ -18,7 +18,7 @@ there exists some $k \in \mathbb{N}$ such thaht given any $n \in \mathbb{N}$ wit
2. Every nonempty set of submodules of $M$ contains a maximal element under inclusion
3. Every submodule of $M$ is finitely-generated
**Collary**. If $R$ is a principal ideal domain (PID), then all nonempty set of ideals of $R$ has a maximal element. Additionally, $R$ is as Noetherian ring.
**Corollary**. If $R$ is a principal ideal domain (PID), then all nonempty set of ideals of $R$ has a maximal element. Additionally, $R$ is as Noetherian ring.
**Proposition**. Let $R$ be an integral doman, and $M$ be a free $R$-module of rank $n < \infty$. Then, given $S$ is subset $M$ with $|S| > n$, the elements of $S$ are $R$-linearly dependent.
@@ -44,7 +44,7 @@ Additionally, if $R$ is a PID, as $\Ann_R(N)$ is an ideal, $\Ann(N) = (n)R$ and
**Definition**. Given any integral domain $R$, the *rank* of an $R$-module $M$ is the maximum number of $R$-linearly independent elements of M.
**Collary**. The rank of a free module is the number of generating elements.
**Corollary**. The rank of a free module is the number of generating elements.
**Theorem**. Let $R$ be a principal ideal domain, and $M$ be a free $R$-module of finite rank $m$, and $N$ be a submodule of $M$. Then,