Number of elements in a factor ring
$begingroup$
I am presented with $f(x) = 2x^3 + 3x^2 + 1$ $in mathbb{Z_5}[x]$ and need to explain why $F = frac{mathbb{Z_5}[x]}{f(x)}$ is a field and also find how many elements are in F.
So far I have shown that $f(x)$ is an irreducible polynomial and I also know that,
If $f(x)$ is an irreducible polynomial in $mathbb{Z_5}[x]$, then the factor ring $frac{mathbb{Z_5}[x]}{f(x)}$ is also a field.
Basically I am not sure how to properly find the factor ring F and also determine how many elements are in it.
Thanks in advance
abstract-algebra
$endgroup$
add a comment |
$begingroup$
I am presented with $f(x) = 2x^3 + 3x^2 + 1$ $in mathbb{Z_5}[x]$ and need to explain why $F = frac{mathbb{Z_5}[x]}{f(x)}$ is a field and also find how many elements are in F.
So far I have shown that $f(x)$ is an irreducible polynomial and I also know that,
If $f(x)$ is an irreducible polynomial in $mathbb{Z_5}[x]$, then the factor ring $frac{mathbb{Z_5}[x]}{f(x)}$ is also a field.
Basically I am not sure how to properly find the factor ring F and also determine how many elements are in it.
Thanks in advance
abstract-algebra
$endgroup$
add a comment |
$begingroup$
I am presented with $f(x) = 2x^3 + 3x^2 + 1$ $in mathbb{Z_5}[x]$ and need to explain why $F = frac{mathbb{Z_5}[x]}{f(x)}$ is a field and also find how many elements are in F.
So far I have shown that $f(x)$ is an irreducible polynomial and I also know that,
If $f(x)$ is an irreducible polynomial in $mathbb{Z_5}[x]$, then the factor ring $frac{mathbb{Z_5}[x]}{f(x)}$ is also a field.
Basically I am not sure how to properly find the factor ring F and also determine how many elements are in it.
Thanks in advance
abstract-algebra
$endgroup$
I am presented with $f(x) = 2x^3 + 3x^2 + 1$ $in mathbb{Z_5}[x]$ and need to explain why $F = frac{mathbb{Z_5}[x]}{f(x)}$ is a field and also find how many elements are in F.
So far I have shown that $f(x)$ is an irreducible polynomial and I also know that,
If $f(x)$ is an irreducible polynomial in $mathbb{Z_5}[x]$, then the factor ring $frac{mathbb{Z_5}[x]}{f(x)}$ is also a field.
Basically I am not sure how to properly find the factor ring F and also determine how many elements are in it.
Thanks in advance
abstract-algebra
abstract-algebra
asked yesterday
MathsRookieMathsRookie
1237
1237
add a comment |
add a comment |
4 Answers
4
active
oldest
votes
$begingroup$
Well, in general, if a field $L$ is an extension field of some field $K$, then $L$ is also a $K$-vector space.
If $f$ is an irreducible polynomial of degree $n$ over, say, ${Bbb Z}_p$, then
the quotient field ${Bbb Z}_p[x]/langle frangle$ has $p^n$ elements and is a vector space over ${Bbb Z}_p$ of dimension $n$.
$endgroup$
add a comment |
$begingroup$
Hint: Use the division algorithm to find canonical representatives for each residue class $g(x) + (f(x))$.
$endgroup$
add a comment |
$begingroup$
Outline:
You know $Bbb Z_5[x]/I$ where $I=langle f(x) rangle $ is a field using the mentioned result. Now, the task is to find $|Bbb Z_5[x]/I |$. Here $Bbb Z_5[x]/I$ can be considered as an entension of $Bbb Z_5$. Also $$dim_Bbb {Z_5} (Bbb Z_5[x]/I)=3=deg f$$
Call ${v_1,v_2,v_3}$ the basis of $Bbb Z_5[x]/I$ over $Bbb Z_5$
Now arbitrarily pick $f(x)+I in Bbb Z_5[x]/I$. Then $$f(x)+I=a_1v_1+a_2v_2+a_3v_3;;;a_i in Bbb Z_5$$
There are $5 times 5 times 5$ choices to choose the coefficients, so $$text{number of such $f(x)+I$ }=5^3=|Bbb Z_5[x]/I|$$
$endgroup$
add a comment |
$begingroup$
Note that two polynomials $g(x)$ and $h(x)$, both of degree 2 or less, will represent different elements in $F$. This is due to the fact that their difference
$g(x)-h(x)$ being of degree less than 3, cannot be a multiple of the cubic polynomials $f(x)=2x^3+3x^2+1$, and so belong to different cosets.
Now a polynomial $h(x)$ of degree 3 or more can be divided by $f(x)$ to get quotient $q(x)$ and remainder $r(x)$
such that $h(x)=q(x)f(x) + r(x)$
Clearly $r(x)$ and $h(x)$ will represent the same coset. This shows that the field $F$ in your question simply consists of polynomials of degree less than $3$. This is easy to count as each coefficient has only a finite number of choices.
$endgroup$
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3179438%2fnumber-of-elements-in-a-factor-ring%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Well, in general, if a field $L$ is an extension field of some field $K$, then $L$ is also a $K$-vector space.
If $f$ is an irreducible polynomial of degree $n$ over, say, ${Bbb Z}_p$, then
the quotient field ${Bbb Z}_p[x]/langle frangle$ has $p^n$ elements and is a vector space over ${Bbb Z}_p$ of dimension $n$.
$endgroup$
add a comment |
$begingroup$
Well, in general, if a field $L$ is an extension field of some field $K$, then $L$ is also a $K$-vector space.
If $f$ is an irreducible polynomial of degree $n$ over, say, ${Bbb Z}_p$, then
the quotient field ${Bbb Z}_p[x]/langle frangle$ has $p^n$ elements and is a vector space over ${Bbb Z}_p$ of dimension $n$.
$endgroup$
add a comment |
$begingroup$
Well, in general, if a field $L$ is an extension field of some field $K$, then $L$ is also a $K$-vector space.
If $f$ is an irreducible polynomial of degree $n$ over, say, ${Bbb Z}_p$, then
the quotient field ${Bbb Z}_p[x]/langle frangle$ has $p^n$ elements and is a vector space over ${Bbb Z}_p$ of dimension $n$.
$endgroup$
Well, in general, if a field $L$ is an extension field of some field $K$, then $L$ is also a $K$-vector space.
If $f$ is an irreducible polynomial of degree $n$ over, say, ${Bbb Z}_p$, then
the quotient field ${Bbb Z}_p[x]/langle frangle$ has $p^n$ elements and is a vector space over ${Bbb Z}_p$ of dimension $n$.
edited yesterday
answered yesterday
WuestenfuxWuestenfux
5,4841513
5,4841513
add a comment |
add a comment |
$begingroup$
Hint: Use the division algorithm to find canonical representatives for each residue class $g(x) + (f(x))$.
$endgroup$
add a comment |
$begingroup$
Hint: Use the division algorithm to find canonical representatives for each residue class $g(x) + (f(x))$.
$endgroup$
add a comment |
$begingroup$
Hint: Use the division algorithm to find canonical representatives for each residue class $g(x) + (f(x))$.
$endgroup$
Hint: Use the division algorithm to find canonical representatives for each residue class $g(x) + (f(x))$.
answered yesterday
lhflhf
167k11172404
167k11172404
add a comment |
add a comment |
$begingroup$
Outline:
You know $Bbb Z_5[x]/I$ where $I=langle f(x) rangle $ is a field using the mentioned result. Now, the task is to find $|Bbb Z_5[x]/I |$. Here $Bbb Z_5[x]/I$ can be considered as an entension of $Bbb Z_5$. Also $$dim_Bbb {Z_5} (Bbb Z_5[x]/I)=3=deg f$$
Call ${v_1,v_2,v_3}$ the basis of $Bbb Z_5[x]/I$ over $Bbb Z_5$
Now arbitrarily pick $f(x)+I in Bbb Z_5[x]/I$. Then $$f(x)+I=a_1v_1+a_2v_2+a_3v_3;;;a_i in Bbb Z_5$$
There are $5 times 5 times 5$ choices to choose the coefficients, so $$text{number of such $f(x)+I$ }=5^3=|Bbb Z_5[x]/I|$$
$endgroup$
add a comment |
$begingroup$
Outline:
You know $Bbb Z_5[x]/I$ where $I=langle f(x) rangle $ is a field using the mentioned result. Now, the task is to find $|Bbb Z_5[x]/I |$. Here $Bbb Z_5[x]/I$ can be considered as an entension of $Bbb Z_5$. Also $$dim_Bbb {Z_5} (Bbb Z_5[x]/I)=3=deg f$$
Call ${v_1,v_2,v_3}$ the basis of $Bbb Z_5[x]/I$ over $Bbb Z_5$
Now arbitrarily pick $f(x)+I in Bbb Z_5[x]/I$. Then $$f(x)+I=a_1v_1+a_2v_2+a_3v_3;;;a_i in Bbb Z_5$$
There are $5 times 5 times 5$ choices to choose the coefficients, so $$text{number of such $f(x)+I$ }=5^3=|Bbb Z_5[x]/I|$$
$endgroup$
add a comment |
$begingroup$
Outline:
You know $Bbb Z_5[x]/I$ where $I=langle f(x) rangle $ is a field using the mentioned result. Now, the task is to find $|Bbb Z_5[x]/I |$. Here $Bbb Z_5[x]/I$ can be considered as an entension of $Bbb Z_5$. Also $$dim_Bbb {Z_5} (Bbb Z_5[x]/I)=3=deg f$$
Call ${v_1,v_2,v_3}$ the basis of $Bbb Z_5[x]/I$ over $Bbb Z_5$
Now arbitrarily pick $f(x)+I in Bbb Z_5[x]/I$. Then $$f(x)+I=a_1v_1+a_2v_2+a_3v_3;;;a_i in Bbb Z_5$$
There are $5 times 5 times 5$ choices to choose the coefficients, so $$text{number of such $f(x)+I$ }=5^3=|Bbb Z_5[x]/I|$$
$endgroup$
Outline:
You know $Bbb Z_5[x]/I$ where $I=langle f(x) rangle $ is a field using the mentioned result. Now, the task is to find $|Bbb Z_5[x]/I |$. Here $Bbb Z_5[x]/I$ can be considered as an entension of $Bbb Z_5$. Also $$dim_Bbb {Z_5} (Bbb Z_5[x]/I)=3=deg f$$
Call ${v_1,v_2,v_3}$ the basis of $Bbb Z_5[x]/I$ over $Bbb Z_5$
Now arbitrarily pick $f(x)+I in Bbb Z_5[x]/I$. Then $$f(x)+I=a_1v_1+a_2v_2+a_3v_3;;;a_i in Bbb Z_5$$
There are $5 times 5 times 5$ choices to choose the coefficients, so $$text{number of such $f(x)+I$ }=5^3=|Bbb Z_5[x]/I|$$
answered yesterday
Chinnapparaj RChinnapparaj R
6,1612929
6,1612929
add a comment |
add a comment |
$begingroup$
Note that two polynomials $g(x)$ and $h(x)$, both of degree 2 or less, will represent different elements in $F$. This is due to the fact that their difference
$g(x)-h(x)$ being of degree less than 3, cannot be a multiple of the cubic polynomials $f(x)=2x^3+3x^2+1$, and so belong to different cosets.
Now a polynomial $h(x)$ of degree 3 or more can be divided by $f(x)$ to get quotient $q(x)$ and remainder $r(x)$
such that $h(x)=q(x)f(x) + r(x)$
Clearly $r(x)$ and $h(x)$ will represent the same coset. This shows that the field $F$ in your question simply consists of polynomials of degree less than $3$. This is easy to count as each coefficient has only a finite number of choices.
$endgroup$
add a comment |
$begingroup$
Note that two polynomials $g(x)$ and $h(x)$, both of degree 2 or less, will represent different elements in $F$. This is due to the fact that their difference
$g(x)-h(x)$ being of degree less than 3, cannot be a multiple of the cubic polynomials $f(x)=2x^3+3x^2+1$, and so belong to different cosets.
Now a polynomial $h(x)$ of degree 3 or more can be divided by $f(x)$ to get quotient $q(x)$ and remainder $r(x)$
such that $h(x)=q(x)f(x) + r(x)$
Clearly $r(x)$ and $h(x)$ will represent the same coset. This shows that the field $F$ in your question simply consists of polynomials of degree less than $3$. This is easy to count as each coefficient has only a finite number of choices.
$endgroup$
add a comment |
$begingroup$
Note that two polynomials $g(x)$ and $h(x)$, both of degree 2 or less, will represent different elements in $F$. This is due to the fact that their difference
$g(x)-h(x)$ being of degree less than 3, cannot be a multiple of the cubic polynomials $f(x)=2x^3+3x^2+1$, and so belong to different cosets.
Now a polynomial $h(x)$ of degree 3 or more can be divided by $f(x)$ to get quotient $q(x)$ and remainder $r(x)$
such that $h(x)=q(x)f(x) + r(x)$
Clearly $r(x)$ and $h(x)$ will represent the same coset. This shows that the field $F$ in your question simply consists of polynomials of degree less than $3$. This is easy to count as each coefficient has only a finite number of choices.
$endgroup$
Note that two polynomials $g(x)$ and $h(x)$, both of degree 2 or less, will represent different elements in $F$. This is due to the fact that their difference
$g(x)-h(x)$ being of degree less than 3, cannot be a multiple of the cubic polynomials $f(x)=2x^3+3x^2+1$, and so belong to different cosets.
Now a polynomial $h(x)$ of degree 3 or more can be divided by $f(x)$ to get quotient $q(x)$ and remainder $r(x)$
such that $h(x)=q(x)f(x) + r(x)$
Clearly $r(x)$ and $h(x)$ will represent the same coset. This shows that the field $F$ in your question simply consists of polynomials of degree less than $3$. This is easy to count as each coefficient has only a finite number of choices.
answered yesterday
P VanchinathanP Vanchinathan
15.5k12136
15.5k12136
add a comment |
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3179438%2fnumber-of-elements-in-a-factor-ring%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown