If $ker fsubset ker g$ where $f,g $ are non-zero linear functionals then show that $f=cg$ for some $cin F$.
$begingroup$
Let $V$ be a vector space with $dim V=n$ .
If $ker fsubset ker g$ where $f,g $ are non-zero linear functionals then show that $f=cg$ for some $cin F$.
Now let $mathcal B={v_1,v_2,ldots ,v_n}$ be a basis of $V$,
since $f,g$ are non-zero linear functionals then $exists v_iin mathcal B $ such that $g(v_i)neq 0implies f(v_i)neq 0$
Take $i=1$ without any loss of generality so take $g(v_1)neq 0,f(v_1)neq 0$.
Now take $c=dfrac{f(v_1)}{g(v_1)}$
Then we need to show that $(f-cg)(v_i)=0forall i$
Now $(f-cg)(v_1)=0$
How to show that $(f-cg)(v_i)=0forall ige 2$
Can someone please help?
Note::Another Question Why do we need the dimension of the vector space to be finite?
linear-algebra vector-spaces linear-transformations
$endgroup$
add a comment |
$begingroup$
Let $V$ be a vector space with $dim V=n$ .
If $ker fsubset ker g$ where $f,g $ are non-zero linear functionals then show that $f=cg$ for some $cin F$.
Now let $mathcal B={v_1,v_2,ldots ,v_n}$ be a basis of $V$,
since $f,g$ are non-zero linear functionals then $exists v_iin mathcal B $ such that $g(v_i)neq 0implies f(v_i)neq 0$
Take $i=1$ without any loss of generality so take $g(v_1)neq 0,f(v_1)neq 0$.
Now take $c=dfrac{f(v_1)}{g(v_1)}$
Then we need to show that $(f-cg)(v_i)=0forall i$
Now $(f-cg)(v_1)=0$
How to show that $(f-cg)(v_i)=0forall ige 2$
Can someone please help?
Note::Another Question Why do we need the dimension of the vector space to be finite?
linear-algebra vector-spaces linear-transformations
$endgroup$
$begingroup$
When you say linear functionals, you mean that $f, g : V rightarrow k$ (where $k$ is the field $V$ is over) right?
$endgroup$
– Aniruddh Agarwal
Dec 23 '18 at 10:40
$begingroup$
@AniruddhAgarwal,yes u r right
$endgroup$
– user596656
Dec 23 '18 at 10:40
$begingroup$
Just realized that this question is a duplicate of this one math.stackexchange.com/questions/60460/…
$endgroup$
– Yanko
Dec 23 '18 at 15:12
add a comment |
$begingroup$
Let $V$ be a vector space with $dim V=n$ .
If $ker fsubset ker g$ where $f,g $ are non-zero linear functionals then show that $f=cg$ for some $cin F$.
Now let $mathcal B={v_1,v_2,ldots ,v_n}$ be a basis of $V$,
since $f,g$ are non-zero linear functionals then $exists v_iin mathcal B $ such that $g(v_i)neq 0implies f(v_i)neq 0$
Take $i=1$ without any loss of generality so take $g(v_1)neq 0,f(v_1)neq 0$.
Now take $c=dfrac{f(v_1)}{g(v_1)}$
Then we need to show that $(f-cg)(v_i)=0forall i$
Now $(f-cg)(v_1)=0$
How to show that $(f-cg)(v_i)=0forall ige 2$
Can someone please help?
Note::Another Question Why do we need the dimension of the vector space to be finite?
linear-algebra vector-spaces linear-transformations
$endgroup$
Let $V$ be a vector space with $dim V=n$ .
If $ker fsubset ker g$ where $f,g $ are non-zero linear functionals then show that $f=cg$ for some $cin F$.
Now let $mathcal B={v_1,v_2,ldots ,v_n}$ be a basis of $V$,
since $f,g$ are non-zero linear functionals then $exists v_iin mathcal B $ such that $g(v_i)neq 0implies f(v_i)neq 0$
Take $i=1$ without any loss of generality so take $g(v_1)neq 0,f(v_1)neq 0$.
Now take $c=dfrac{f(v_1)}{g(v_1)}$
Then we need to show that $(f-cg)(v_i)=0forall i$
Now $(f-cg)(v_1)=0$
How to show that $(f-cg)(v_i)=0forall ige 2$
Can someone please help?
Note::Another Question Why do we need the dimension of the vector space to be finite?
linear-algebra vector-spaces linear-transformations
linear-algebra vector-spaces linear-transformations
asked Dec 23 '18 at 10:36
user596656
$begingroup$
When you say linear functionals, you mean that $f, g : V rightarrow k$ (where $k$ is the field $V$ is over) right?
$endgroup$
– Aniruddh Agarwal
Dec 23 '18 at 10:40
$begingroup$
@AniruddhAgarwal,yes u r right
$endgroup$
– user596656
Dec 23 '18 at 10:40
$begingroup$
Just realized that this question is a duplicate of this one math.stackexchange.com/questions/60460/…
$endgroup$
– Yanko
Dec 23 '18 at 15:12
add a comment |
$begingroup$
When you say linear functionals, you mean that $f, g : V rightarrow k$ (where $k$ is the field $V$ is over) right?
$endgroup$
– Aniruddh Agarwal
Dec 23 '18 at 10:40
$begingroup$
@AniruddhAgarwal,yes u r right
$endgroup$
– user596656
Dec 23 '18 at 10:40
$begingroup$
Just realized that this question is a duplicate of this one math.stackexchange.com/questions/60460/…
$endgroup$
– Yanko
Dec 23 '18 at 15:12
$begingroup$
When you say linear functionals, you mean that $f, g : V rightarrow k$ (where $k$ is the field $V$ is over) right?
$endgroup$
– Aniruddh Agarwal
Dec 23 '18 at 10:40
$begingroup$
When you say linear functionals, you mean that $f, g : V rightarrow k$ (where $k$ is the field $V$ is over) right?
$endgroup$
– Aniruddh Agarwal
Dec 23 '18 at 10:40
$begingroup$
@AniruddhAgarwal,yes u r right
$endgroup$
– user596656
Dec 23 '18 at 10:40
$begingroup$
@AniruddhAgarwal,yes u r right
$endgroup$
– user596656
Dec 23 '18 at 10:40
$begingroup$
Just realized that this question is a duplicate of this one math.stackexchange.com/questions/60460/…
$endgroup$
– Yanko
Dec 23 '18 at 15:12
$begingroup$
Just realized that this question is a duplicate of this one math.stackexchange.com/questions/60460/…
$endgroup$
– Yanko
Dec 23 '18 at 15:12
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
There is no need for finite dimensionality and no need to use bases. Let $f(x) neq 0$, $y$ be arbitrary and consider $y-frac {f(y)} {f(x)} x$. By linearity we get $f(y-frac {f(y)} {f(x)} x)=0$. By hypothesis this implies $g(y-frac {f(y)} {f(x)} x)=0$. Hence $g(y)=cf(y)$ where $c=frac {g(x)} {f(x)}$. Hypothesis implies that $c neq 0$ so we can write $f=frac 1 c g$.
$endgroup$
1
$begingroup$
Did you switch up $f$ and $g$?
$endgroup$
– Shubham Johri
Dec 23 '18 at 15:09
$begingroup$
@ShubhamJohri Thanks for the comment. I have corrected the answer.
$endgroup$
– Kavi Rama Murthy
Dec 23 '18 at 23:15
add a comment |
$begingroup$
Let me provide another approach: (it might be used to solve the problem with your last line but it is completely independent to your approach).
By definition $f,g:Vrightarrowmathbb{R}$ are non-zero linear functionals (you can replace $mathbb{R}$ with $mathbb{C}$ or any field). By the rank-nullity theorem we have that $dim ker f = dim ker g = n-1$ Since $ker f subseteq ker g$ we conclude that $ker f = ker g$. (In some sense this shows that $f-cg(v_i)=0$ in your solution because $f(v_i)=g(v_i)=0$.)
Now take a basis $v_1,...,v_{n-1}$ for the kernel and take $v$ which is linearily independent of those. Then $f(v),g(v)not = 0$ are real numbers.
Take $c=frac{f(v)}{g(v)}$. Since $f,g$ are non-zero only on $text{span} ({v})$ the rest of the claim is immediate
$endgroup$
$begingroup$
Nice approach !it does not answer for the infinite dimensional case
$endgroup$
– user596656
Dec 23 '18 at 12:03
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%2f3050228%2fif-ker-f-subset-ker-g-where-f-g-are-non-zero-linear-functionals-then-show%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
There is no need for finite dimensionality and no need to use bases. Let $f(x) neq 0$, $y$ be arbitrary and consider $y-frac {f(y)} {f(x)} x$. By linearity we get $f(y-frac {f(y)} {f(x)} x)=0$. By hypothesis this implies $g(y-frac {f(y)} {f(x)} x)=0$. Hence $g(y)=cf(y)$ where $c=frac {g(x)} {f(x)}$. Hypothesis implies that $c neq 0$ so we can write $f=frac 1 c g$.
$endgroup$
1
$begingroup$
Did you switch up $f$ and $g$?
$endgroup$
– Shubham Johri
Dec 23 '18 at 15:09
$begingroup$
@ShubhamJohri Thanks for the comment. I have corrected the answer.
$endgroup$
– Kavi Rama Murthy
Dec 23 '18 at 23:15
add a comment |
$begingroup$
There is no need for finite dimensionality and no need to use bases. Let $f(x) neq 0$, $y$ be arbitrary and consider $y-frac {f(y)} {f(x)} x$. By linearity we get $f(y-frac {f(y)} {f(x)} x)=0$. By hypothesis this implies $g(y-frac {f(y)} {f(x)} x)=0$. Hence $g(y)=cf(y)$ where $c=frac {g(x)} {f(x)}$. Hypothesis implies that $c neq 0$ so we can write $f=frac 1 c g$.
$endgroup$
1
$begingroup$
Did you switch up $f$ and $g$?
$endgroup$
– Shubham Johri
Dec 23 '18 at 15:09
$begingroup$
@ShubhamJohri Thanks for the comment. I have corrected the answer.
$endgroup$
– Kavi Rama Murthy
Dec 23 '18 at 23:15
add a comment |
$begingroup$
There is no need for finite dimensionality and no need to use bases. Let $f(x) neq 0$, $y$ be arbitrary and consider $y-frac {f(y)} {f(x)} x$. By linearity we get $f(y-frac {f(y)} {f(x)} x)=0$. By hypothesis this implies $g(y-frac {f(y)} {f(x)} x)=0$. Hence $g(y)=cf(y)$ where $c=frac {g(x)} {f(x)}$. Hypothesis implies that $c neq 0$ so we can write $f=frac 1 c g$.
$endgroup$
There is no need for finite dimensionality and no need to use bases. Let $f(x) neq 0$, $y$ be arbitrary and consider $y-frac {f(y)} {f(x)} x$. By linearity we get $f(y-frac {f(y)} {f(x)} x)=0$. By hypothesis this implies $g(y-frac {f(y)} {f(x)} x)=0$. Hence $g(y)=cf(y)$ where $c=frac {g(x)} {f(x)}$. Hypothesis implies that $c neq 0$ so we can write $f=frac 1 c g$.
edited Dec 24 '18 at 6:08
answered Dec 23 '18 at 11:49
Kavi Rama MurthyKavi Rama Murthy
64.8k42766
64.8k42766
1
$begingroup$
Did you switch up $f$ and $g$?
$endgroup$
– Shubham Johri
Dec 23 '18 at 15:09
$begingroup$
@ShubhamJohri Thanks for the comment. I have corrected the answer.
$endgroup$
– Kavi Rama Murthy
Dec 23 '18 at 23:15
add a comment |
1
$begingroup$
Did you switch up $f$ and $g$?
$endgroup$
– Shubham Johri
Dec 23 '18 at 15:09
$begingroup$
@ShubhamJohri Thanks for the comment. I have corrected the answer.
$endgroup$
– Kavi Rama Murthy
Dec 23 '18 at 23:15
1
1
$begingroup$
Did you switch up $f$ and $g$?
$endgroup$
– Shubham Johri
Dec 23 '18 at 15:09
$begingroup$
Did you switch up $f$ and $g$?
$endgroup$
– Shubham Johri
Dec 23 '18 at 15:09
$begingroup$
@ShubhamJohri Thanks for the comment. I have corrected the answer.
$endgroup$
– Kavi Rama Murthy
Dec 23 '18 at 23:15
$begingroup$
@ShubhamJohri Thanks for the comment. I have corrected the answer.
$endgroup$
– Kavi Rama Murthy
Dec 23 '18 at 23:15
add a comment |
$begingroup$
Let me provide another approach: (it might be used to solve the problem with your last line but it is completely independent to your approach).
By definition $f,g:Vrightarrowmathbb{R}$ are non-zero linear functionals (you can replace $mathbb{R}$ with $mathbb{C}$ or any field). By the rank-nullity theorem we have that $dim ker f = dim ker g = n-1$ Since $ker f subseteq ker g$ we conclude that $ker f = ker g$. (In some sense this shows that $f-cg(v_i)=0$ in your solution because $f(v_i)=g(v_i)=0$.)
Now take a basis $v_1,...,v_{n-1}$ for the kernel and take $v$ which is linearily independent of those. Then $f(v),g(v)not = 0$ are real numbers.
Take $c=frac{f(v)}{g(v)}$. Since $f,g$ are non-zero only on $text{span} ({v})$ the rest of the claim is immediate
$endgroup$
$begingroup$
Nice approach !it does not answer for the infinite dimensional case
$endgroup$
– user596656
Dec 23 '18 at 12:03
add a comment |
$begingroup$
Let me provide another approach: (it might be used to solve the problem with your last line but it is completely independent to your approach).
By definition $f,g:Vrightarrowmathbb{R}$ are non-zero linear functionals (you can replace $mathbb{R}$ with $mathbb{C}$ or any field). By the rank-nullity theorem we have that $dim ker f = dim ker g = n-1$ Since $ker f subseteq ker g$ we conclude that $ker f = ker g$. (In some sense this shows that $f-cg(v_i)=0$ in your solution because $f(v_i)=g(v_i)=0$.)
Now take a basis $v_1,...,v_{n-1}$ for the kernel and take $v$ which is linearily independent of those. Then $f(v),g(v)not = 0$ are real numbers.
Take $c=frac{f(v)}{g(v)}$. Since $f,g$ are non-zero only on $text{span} ({v})$ the rest of the claim is immediate
$endgroup$
$begingroup$
Nice approach !it does not answer for the infinite dimensional case
$endgroup$
– user596656
Dec 23 '18 at 12:03
add a comment |
$begingroup$
Let me provide another approach: (it might be used to solve the problem with your last line but it is completely independent to your approach).
By definition $f,g:Vrightarrowmathbb{R}$ are non-zero linear functionals (you can replace $mathbb{R}$ with $mathbb{C}$ or any field). By the rank-nullity theorem we have that $dim ker f = dim ker g = n-1$ Since $ker f subseteq ker g$ we conclude that $ker f = ker g$. (In some sense this shows that $f-cg(v_i)=0$ in your solution because $f(v_i)=g(v_i)=0$.)
Now take a basis $v_1,...,v_{n-1}$ for the kernel and take $v$ which is linearily independent of those. Then $f(v),g(v)not = 0$ are real numbers.
Take $c=frac{f(v)}{g(v)}$. Since $f,g$ are non-zero only on $text{span} ({v})$ the rest of the claim is immediate
$endgroup$
Let me provide another approach: (it might be used to solve the problem with your last line but it is completely independent to your approach).
By definition $f,g:Vrightarrowmathbb{R}$ are non-zero linear functionals (you can replace $mathbb{R}$ with $mathbb{C}$ or any field). By the rank-nullity theorem we have that $dim ker f = dim ker g = n-1$ Since $ker f subseteq ker g$ we conclude that $ker f = ker g$. (In some sense this shows that $f-cg(v_i)=0$ in your solution because $f(v_i)=g(v_i)=0$.)
Now take a basis $v_1,...,v_{n-1}$ for the kernel and take $v$ which is linearily independent of those. Then $f(v),g(v)not = 0$ are real numbers.
Take $c=frac{f(v)}{g(v)}$. Since $f,g$ are non-zero only on $text{span} ({v})$ the rest of the claim is immediate
answered Dec 23 '18 at 11:16
YankoYanko
7,4801729
7,4801729
$begingroup$
Nice approach !it does not answer for the infinite dimensional case
$endgroup$
– user596656
Dec 23 '18 at 12:03
add a comment |
$begingroup$
Nice approach !it does not answer for the infinite dimensional case
$endgroup$
– user596656
Dec 23 '18 at 12:03
$begingroup$
Nice approach !it does not answer for the infinite dimensional case
$endgroup$
– user596656
Dec 23 '18 at 12:03
$begingroup$
Nice approach !it does not answer for the infinite dimensional case
$endgroup$
– user596656
Dec 23 '18 at 12:03
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%2f3050228%2fif-ker-f-subset-ker-g-where-f-g-are-non-zero-linear-functionals-then-show%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
$begingroup$
When you say linear functionals, you mean that $f, g : V rightarrow k$ (where $k$ is the field $V$ is over) right?
$endgroup$
– Aniruddh Agarwal
Dec 23 '18 at 10:40
$begingroup$
@AniruddhAgarwal,yes u r right
$endgroup$
– user596656
Dec 23 '18 at 10:40
$begingroup$
Just realized that this question is a duplicate of this one math.stackexchange.com/questions/60460/…
$endgroup$
– Yanko
Dec 23 '18 at 15:12