Let $f:mathbb{I} to mathbb{R}$ continuous function such that $f(0)=f(1)$.











up vote
1
down vote

favorite












$mathbb{I} = [0,1]$



Let $f:mathbb{I} to mathbb{R}$ continuous function such that $f(0)=f(1)$. Prove that for all $n in mathbb{N} $ there $ x in mathbb{I}$ such that $ x + frac{1}{n} in mathbb{I}$ and $f( x + frac{1}{n})=f(x)$



Could you help me by giving me an idea of ​​how to do it?










share|cite|improve this question
























  • No derivatives, but maybe there's a theorem we can use to show that $f(x+1/n)-f(x)$ has at least one zero on $mathbb{I}$.
    – Prototank
    Nov 16 at 2:00










  • No, only this is questions and it is about of continuous function
    – Walys Herrera
    Nov 16 at 2:00










  • Any hunch? What was your 1st idea when see this? What have you learned?
    – xbh
    Nov 16 at 2:01










  • I think that i should work with succesiones for the $frac{1}{n} + x $
    – Walys Herrera
    Nov 16 at 2:03










  • Is that induction?
    – Prototank
    Nov 16 at 2:05















up vote
1
down vote

favorite












$mathbb{I} = [0,1]$



Let $f:mathbb{I} to mathbb{R}$ continuous function such that $f(0)=f(1)$. Prove that for all $n in mathbb{N} $ there $ x in mathbb{I}$ such that $ x + frac{1}{n} in mathbb{I}$ and $f( x + frac{1}{n})=f(x)$



Could you help me by giving me an idea of ​​how to do it?










share|cite|improve this question
























  • No derivatives, but maybe there's a theorem we can use to show that $f(x+1/n)-f(x)$ has at least one zero on $mathbb{I}$.
    – Prototank
    Nov 16 at 2:00










  • No, only this is questions and it is about of continuous function
    – Walys Herrera
    Nov 16 at 2:00










  • Any hunch? What was your 1st idea when see this? What have you learned?
    – xbh
    Nov 16 at 2:01










  • I think that i should work with succesiones for the $frac{1}{n} + x $
    – Walys Herrera
    Nov 16 at 2:03










  • Is that induction?
    – Prototank
    Nov 16 at 2:05













up vote
1
down vote

favorite









up vote
1
down vote

favorite











$mathbb{I} = [0,1]$



Let $f:mathbb{I} to mathbb{R}$ continuous function such that $f(0)=f(1)$. Prove that for all $n in mathbb{N} $ there $ x in mathbb{I}$ such that $ x + frac{1}{n} in mathbb{I}$ and $f( x + frac{1}{n})=f(x)$



Could you help me by giving me an idea of ​​how to do it?










share|cite|improve this question















$mathbb{I} = [0,1]$



Let $f:mathbb{I} to mathbb{R}$ continuous function such that $f(0)=f(1)$. Prove that for all $n in mathbb{N} $ there $ x in mathbb{I}$ such that $ x + frac{1}{n} in mathbb{I}$ and $f( x + frac{1}{n})=f(x)$



Could you help me by giving me an idea of ​​how to do it?







real-analysis general-topology functions continuity






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Nov 16 at 1:50

























asked Nov 16 at 1:45









Walys Herrera

63




63












  • No derivatives, but maybe there's a theorem we can use to show that $f(x+1/n)-f(x)$ has at least one zero on $mathbb{I}$.
    – Prototank
    Nov 16 at 2:00










  • No, only this is questions and it is about of continuous function
    – Walys Herrera
    Nov 16 at 2:00










  • Any hunch? What was your 1st idea when see this? What have you learned?
    – xbh
    Nov 16 at 2:01










  • I think that i should work with succesiones for the $frac{1}{n} + x $
    – Walys Herrera
    Nov 16 at 2:03










  • Is that induction?
    – Prototank
    Nov 16 at 2:05


















  • No derivatives, but maybe there's a theorem we can use to show that $f(x+1/n)-f(x)$ has at least one zero on $mathbb{I}$.
    – Prototank
    Nov 16 at 2:00










  • No, only this is questions and it is about of continuous function
    – Walys Herrera
    Nov 16 at 2:00










  • Any hunch? What was your 1st idea when see this? What have you learned?
    – xbh
    Nov 16 at 2:01










  • I think that i should work with succesiones for the $frac{1}{n} + x $
    – Walys Herrera
    Nov 16 at 2:03










  • Is that induction?
    – Prototank
    Nov 16 at 2:05
















No derivatives, but maybe there's a theorem we can use to show that $f(x+1/n)-f(x)$ has at least one zero on $mathbb{I}$.
– Prototank
Nov 16 at 2:00




No derivatives, but maybe there's a theorem we can use to show that $f(x+1/n)-f(x)$ has at least one zero on $mathbb{I}$.
– Prototank
Nov 16 at 2:00












No, only this is questions and it is about of continuous function
– Walys Herrera
Nov 16 at 2:00




No, only this is questions and it is about of continuous function
– Walys Herrera
Nov 16 at 2:00












Any hunch? What was your 1st idea when see this? What have you learned?
– xbh
Nov 16 at 2:01




Any hunch? What was your 1st idea when see this? What have you learned?
– xbh
Nov 16 at 2:01












I think that i should work with succesiones for the $frac{1}{n} + x $
– Walys Herrera
Nov 16 at 2:03




I think that i should work with succesiones for the $frac{1}{n} + x $
– Walys Herrera
Nov 16 at 2:03












Is that induction?
– Prototank
Nov 16 at 2:05




Is that induction?
– Prototank
Nov 16 at 2:05










2 Answers
2






active

oldest

votes

















up vote
4
down vote













Suppose there is no such $x$. Then either $f(x+frac 1 n ) >f(x)$ for all $x$ or $f(x+frac 1 n ) <f(x)$ for all $x$ (by IVP applied to the continuous function $f(x+frac 1 n ) -f(x))$. Assume that $f(x+frac 1 n ) >f(x)$ for all $x$. (the proof is similar in the other case). Then $f(0)<f(frac 1 n) <f(frac 2 n)<cdots <f(1)$ which is a contradiction.






share|cite|improve this answer




























    up vote
    0
    down vote













    Extend $f$ to $mathbb{R}$ periodically (and so continuously by $f(0) = f(1)$). Let $g(x): = f(x+1/n) - f(x)$. Then we have
    $$
    g(x) + gleft(x+frac{1}{n}right) + cdots + gleft(x + frac{n-1}{n}right) = 0
    $$

    This implies that $g(x)$ can't have always same sign, and so $g$ has a zero by intermediate value theorem.



    I'm sure that there's better way to show that $f(x+alpha) = f(x)$ has root for any $0<alpha < 1$, since this method only works for $alphain mathbb{Q}$. But I don't have any idea for this now.






    share|cite|improve this answer





















    • Continuity implies what you conjecture, plus compactness of $mathbb{I}$, I think.
      – Prototank
      Nov 16 at 2:07












    • @Prototank I think we have to be careful. If $r_{n}$ is a sequence of rational numbers that converges to $alpha$, then $g_{n}(x) = f(x+r_{n}) -f(x)$ has a solution $c_{n}$ for all $n$, but this doesn't imply that $c_{n}$ converges for some number.
      – Seewoo Lee
      Nov 16 at 2:13






    • 1




      The sequence of $r_n$ converges to $alpha$. Each $r_n$, by your argument, gives an $x_n$ where $f(x_n+r_n)-f(x_n)=0$. The function $G:Ktomathbb{R}$ by $G(x,y)=f(x+y)-f(x)$ is continuous and zero on the sequence $(x_n,r_n)$. I think $K$ needs to be the 2-simplex, the region $K=lbrace (x,y):x,ygeq 0 x+yleq 1rbrace$. Choose a convergent subsequence in $K$. How does that look?
      – Prototank
      Nov 16 at 2:23












    • @Prototank That seems good for me. Thanks!
      – Seewoo Lee
      Nov 16 at 3:37










    • But f is only defined for $[0,1]$, your proof is incomplete until you show that the zero of g is in $[0, 1-1/n]$. Moreover, if you use an $alpha$ other than some $1/n$ the claim is false (even if $alpha$ is rational). Let p be a periodic function whose period is such an $alpha$, ($0 < alpha < 1$), and $p(0) = 0$, $p(1) = c neq 0$. Let $f(x) = p(x) - cx$. Then $f(0) = f(1) = 0$ and $f(x + alpha) - f(x) = -calpha neq 0$ for all $x in [0, 1-alpha]$.
      – David Hartley
      Nov 17 at 2:14











    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',
    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
    });


    }
    });














     

    draft saved


    draft discarded


















    StackExchange.ready(
    function () {
    StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3000603%2flet-f-mathbbi-to-mathbbr-continuous-function-such-that-f0-f1%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








    up vote
    4
    down vote













    Suppose there is no such $x$. Then either $f(x+frac 1 n ) >f(x)$ for all $x$ or $f(x+frac 1 n ) <f(x)$ for all $x$ (by IVP applied to the continuous function $f(x+frac 1 n ) -f(x))$. Assume that $f(x+frac 1 n ) >f(x)$ for all $x$. (the proof is similar in the other case). Then $f(0)<f(frac 1 n) <f(frac 2 n)<cdots <f(1)$ which is a contradiction.






    share|cite|improve this answer

























      up vote
      4
      down vote













      Suppose there is no such $x$. Then either $f(x+frac 1 n ) >f(x)$ for all $x$ or $f(x+frac 1 n ) <f(x)$ for all $x$ (by IVP applied to the continuous function $f(x+frac 1 n ) -f(x))$. Assume that $f(x+frac 1 n ) >f(x)$ for all $x$. (the proof is similar in the other case). Then $f(0)<f(frac 1 n) <f(frac 2 n)<cdots <f(1)$ which is a contradiction.






      share|cite|improve this answer























        up vote
        4
        down vote










        up vote
        4
        down vote









        Suppose there is no such $x$. Then either $f(x+frac 1 n ) >f(x)$ for all $x$ or $f(x+frac 1 n ) <f(x)$ for all $x$ (by IVP applied to the continuous function $f(x+frac 1 n ) -f(x))$. Assume that $f(x+frac 1 n ) >f(x)$ for all $x$. (the proof is similar in the other case). Then $f(0)<f(frac 1 n) <f(frac 2 n)<cdots <f(1)$ which is a contradiction.






        share|cite|improve this answer












        Suppose there is no such $x$. Then either $f(x+frac 1 n ) >f(x)$ for all $x$ or $f(x+frac 1 n ) <f(x)$ for all $x$ (by IVP applied to the continuous function $f(x+frac 1 n ) -f(x))$. Assume that $f(x+frac 1 n ) >f(x)$ for all $x$. (the proof is similar in the other case). Then $f(0)<f(frac 1 n) <f(frac 2 n)<cdots <f(1)$ which is a contradiction.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Nov 16 at 5:38









        Kavi Rama Murthy

        42.1k31751




        42.1k31751






















            up vote
            0
            down vote













            Extend $f$ to $mathbb{R}$ periodically (and so continuously by $f(0) = f(1)$). Let $g(x): = f(x+1/n) - f(x)$. Then we have
            $$
            g(x) + gleft(x+frac{1}{n}right) + cdots + gleft(x + frac{n-1}{n}right) = 0
            $$

            This implies that $g(x)$ can't have always same sign, and so $g$ has a zero by intermediate value theorem.



            I'm sure that there's better way to show that $f(x+alpha) = f(x)$ has root for any $0<alpha < 1$, since this method only works for $alphain mathbb{Q}$. But I don't have any idea for this now.






            share|cite|improve this answer





















            • Continuity implies what you conjecture, plus compactness of $mathbb{I}$, I think.
              – Prototank
              Nov 16 at 2:07












            • @Prototank I think we have to be careful. If $r_{n}$ is a sequence of rational numbers that converges to $alpha$, then $g_{n}(x) = f(x+r_{n}) -f(x)$ has a solution $c_{n}$ for all $n$, but this doesn't imply that $c_{n}$ converges for some number.
              – Seewoo Lee
              Nov 16 at 2:13






            • 1




              The sequence of $r_n$ converges to $alpha$. Each $r_n$, by your argument, gives an $x_n$ where $f(x_n+r_n)-f(x_n)=0$. The function $G:Ktomathbb{R}$ by $G(x,y)=f(x+y)-f(x)$ is continuous and zero on the sequence $(x_n,r_n)$. I think $K$ needs to be the 2-simplex, the region $K=lbrace (x,y):x,ygeq 0 x+yleq 1rbrace$. Choose a convergent subsequence in $K$. How does that look?
              – Prototank
              Nov 16 at 2:23












            • @Prototank That seems good for me. Thanks!
              – Seewoo Lee
              Nov 16 at 3:37










            • But f is only defined for $[0,1]$, your proof is incomplete until you show that the zero of g is in $[0, 1-1/n]$. Moreover, if you use an $alpha$ other than some $1/n$ the claim is false (even if $alpha$ is rational). Let p be a periodic function whose period is such an $alpha$, ($0 < alpha < 1$), and $p(0) = 0$, $p(1) = c neq 0$. Let $f(x) = p(x) - cx$. Then $f(0) = f(1) = 0$ and $f(x + alpha) - f(x) = -calpha neq 0$ for all $x in [0, 1-alpha]$.
              – David Hartley
              Nov 17 at 2:14















            up vote
            0
            down vote













            Extend $f$ to $mathbb{R}$ periodically (and so continuously by $f(0) = f(1)$). Let $g(x): = f(x+1/n) - f(x)$. Then we have
            $$
            g(x) + gleft(x+frac{1}{n}right) + cdots + gleft(x + frac{n-1}{n}right) = 0
            $$

            This implies that $g(x)$ can't have always same sign, and so $g$ has a zero by intermediate value theorem.



            I'm sure that there's better way to show that $f(x+alpha) = f(x)$ has root for any $0<alpha < 1$, since this method only works for $alphain mathbb{Q}$. But I don't have any idea for this now.






            share|cite|improve this answer





















            • Continuity implies what you conjecture, plus compactness of $mathbb{I}$, I think.
              – Prototank
              Nov 16 at 2:07












            • @Prototank I think we have to be careful. If $r_{n}$ is a sequence of rational numbers that converges to $alpha$, then $g_{n}(x) = f(x+r_{n}) -f(x)$ has a solution $c_{n}$ for all $n$, but this doesn't imply that $c_{n}$ converges for some number.
              – Seewoo Lee
              Nov 16 at 2:13






            • 1




              The sequence of $r_n$ converges to $alpha$. Each $r_n$, by your argument, gives an $x_n$ where $f(x_n+r_n)-f(x_n)=0$. The function $G:Ktomathbb{R}$ by $G(x,y)=f(x+y)-f(x)$ is continuous and zero on the sequence $(x_n,r_n)$. I think $K$ needs to be the 2-simplex, the region $K=lbrace (x,y):x,ygeq 0 x+yleq 1rbrace$. Choose a convergent subsequence in $K$. How does that look?
              – Prototank
              Nov 16 at 2:23












            • @Prototank That seems good for me. Thanks!
              – Seewoo Lee
              Nov 16 at 3:37










            • But f is only defined for $[0,1]$, your proof is incomplete until you show that the zero of g is in $[0, 1-1/n]$. Moreover, if you use an $alpha$ other than some $1/n$ the claim is false (even if $alpha$ is rational). Let p be a periodic function whose period is such an $alpha$, ($0 < alpha < 1$), and $p(0) = 0$, $p(1) = c neq 0$. Let $f(x) = p(x) - cx$. Then $f(0) = f(1) = 0$ and $f(x + alpha) - f(x) = -calpha neq 0$ for all $x in [0, 1-alpha]$.
              – David Hartley
              Nov 17 at 2:14













            up vote
            0
            down vote










            up vote
            0
            down vote









            Extend $f$ to $mathbb{R}$ periodically (and so continuously by $f(0) = f(1)$). Let $g(x): = f(x+1/n) - f(x)$. Then we have
            $$
            g(x) + gleft(x+frac{1}{n}right) + cdots + gleft(x + frac{n-1}{n}right) = 0
            $$

            This implies that $g(x)$ can't have always same sign, and so $g$ has a zero by intermediate value theorem.



            I'm sure that there's better way to show that $f(x+alpha) = f(x)$ has root for any $0<alpha < 1$, since this method only works for $alphain mathbb{Q}$. But I don't have any idea for this now.






            share|cite|improve this answer












            Extend $f$ to $mathbb{R}$ periodically (and so continuously by $f(0) = f(1)$). Let $g(x): = f(x+1/n) - f(x)$. Then we have
            $$
            g(x) + gleft(x+frac{1}{n}right) + cdots + gleft(x + frac{n-1}{n}right) = 0
            $$

            This implies that $g(x)$ can't have always same sign, and so $g$ has a zero by intermediate value theorem.



            I'm sure that there's better way to show that $f(x+alpha) = f(x)$ has root for any $0<alpha < 1$, since this method only works for $alphain mathbb{Q}$. But I don't have any idea for this now.







            share|cite|improve this answer












            share|cite|improve this answer



            share|cite|improve this answer










            answered Nov 16 at 2:06









            Seewoo Lee

            5,941826




            5,941826












            • Continuity implies what you conjecture, plus compactness of $mathbb{I}$, I think.
              – Prototank
              Nov 16 at 2:07












            • @Prototank I think we have to be careful. If $r_{n}$ is a sequence of rational numbers that converges to $alpha$, then $g_{n}(x) = f(x+r_{n}) -f(x)$ has a solution $c_{n}$ for all $n$, but this doesn't imply that $c_{n}$ converges for some number.
              – Seewoo Lee
              Nov 16 at 2:13






            • 1




              The sequence of $r_n$ converges to $alpha$. Each $r_n$, by your argument, gives an $x_n$ where $f(x_n+r_n)-f(x_n)=0$. The function $G:Ktomathbb{R}$ by $G(x,y)=f(x+y)-f(x)$ is continuous and zero on the sequence $(x_n,r_n)$. I think $K$ needs to be the 2-simplex, the region $K=lbrace (x,y):x,ygeq 0 x+yleq 1rbrace$. Choose a convergent subsequence in $K$. How does that look?
              – Prototank
              Nov 16 at 2:23












            • @Prototank That seems good for me. Thanks!
              – Seewoo Lee
              Nov 16 at 3:37










            • But f is only defined for $[0,1]$, your proof is incomplete until you show that the zero of g is in $[0, 1-1/n]$. Moreover, if you use an $alpha$ other than some $1/n$ the claim is false (even if $alpha$ is rational). Let p be a periodic function whose period is such an $alpha$, ($0 < alpha < 1$), and $p(0) = 0$, $p(1) = c neq 0$. Let $f(x) = p(x) - cx$. Then $f(0) = f(1) = 0$ and $f(x + alpha) - f(x) = -calpha neq 0$ for all $x in [0, 1-alpha]$.
              – David Hartley
              Nov 17 at 2:14


















            • Continuity implies what you conjecture, plus compactness of $mathbb{I}$, I think.
              – Prototank
              Nov 16 at 2:07












            • @Prototank I think we have to be careful. If $r_{n}$ is a sequence of rational numbers that converges to $alpha$, then $g_{n}(x) = f(x+r_{n}) -f(x)$ has a solution $c_{n}$ for all $n$, but this doesn't imply that $c_{n}$ converges for some number.
              – Seewoo Lee
              Nov 16 at 2:13






            • 1




              The sequence of $r_n$ converges to $alpha$. Each $r_n$, by your argument, gives an $x_n$ where $f(x_n+r_n)-f(x_n)=0$. The function $G:Ktomathbb{R}$ by $G(x,y)=f(x+y)-f(x)$ is continuous and zero on the sequence $(x_n,r_n)$. I think $K$ needs to be the 2-simplex, the region $K=lbrace (x,y):x,ygeq 0 x+yleq 1rbrace$. Choose a convergent subsequence in $K$. How does that look?
              – Prototank
              Nov 16 at 2:23












            • @Prototank That seems good for me. Thanks!
              – Seewoo Lee
              Nov 16 at 3:37










            • But f is only defined for $[0,1]$, your proof is incomplete until you show that the zero of g is in $[0, 1-1/n]$. Moreover, if you use an $alpha$ other than some $1/n$ the claim is false (even if $alpha$ is rational). Let p be a periodic function whose period is such an $alpha$, ($0 < alpha < 1$), and $p(0) = 0$, $p(1) = c neq 0$. Let $f(x) = p(x) - cx$. Then $f(0) = f(1) = 0$ and $f(x + alpha) - f(x) = -calpha neq 0$ for all $x in [0, 1-alpha]$.
              – David Hartley
              Nov 17 at 2:14
















            Continuity implies what you conjecture, plus compactness of $mathbb{I}$, I think.
            – Prototank
            Nov 16 at 2:07






            Continuity implies what you conjecture, plus compactness of $mathbb{I}$, I think.
            – Prototank
            Nov 16 at 2:07














            @Prototank I think we have to be careful. If $r_{n}$ is a sequence of rational numbers that converges to $alpha$, then $g_{n}(x) = f(x+r_{n}) -f(x)$ has a solution $c_{n}$ for all $n$, but this doesn't imply that $c_{n}$ converges for some number.
            – Seewoo Lee
            Nov 16 at 2:13




            @Prototank I think we have to be careful. If $r_{n}$ is a sequence of rational numbers that converges to $alpha$, then $g_{n}(x) = f(x+r_{n}) -f(x)$ has a solution $c_{n}$ for all $n$, but this doesn't imply that $c_{n}$ converges for some number.
            – Seewoo Lee
            Nov 16 at 2:13




            1




            1




            The sequence of $r_n$ converges to $alpha$. Each $r_n$, by your argument, gives an $x_n$ where $f(x_n+r_n)-f(x_n)=0$. The function $G:Ktomathbb{R}$ by $G(x,y)=f(x+y)-f(x)$ is continuous and zero on the sequence $(x_n,r_n)$. I think $K$ needs to be the 2-simplex, the region $K=lbrace (x,y):x,ygeq 0 x+yleq 1rbrace$. Choose a convergent subsequence in $K$. How does that look?
            – Prototank
            Nov 16 at 2:23






            The sequence of $r_n$ converges to $alpha$. Each $r_n$, by your argument, gives an $x_n$ where $f(x_n+r_n)-f(x_n)=0$. The function $G:Ktomathbb{R}$ by $G(x,y)=f(x+y)-f(x)$ is continuous and zero on the sequence $(x_n,r_n)$. I think $K$ needs to be the 2-simplex, the region $K=lbrace (x,y):x,ygeq 0 x+yleq 1rbrace$. Choose a convergent subsequence in $K$. How does that look?
            – Prototank
            Nov 16 at 2:23














            @Prototank That seems good for me. Thanks!
            – Seewoo Lee
            Nov 16 at 3:37




            @Prototank That seems good for me. Thanks!
            – Seewoo Lee
            Nov 16 at 3:37












            But f is only defined for $[0,1]$, your proof is incomplete until you show that the zero of g is in $[0, 1-1/n]$. Moreover, if you use an $alpha$ other than some $1/n$ the claim is false (even if $alpha$ is rational). Let p be a periodic function whose period is such an $alpha$, ($0 < alpha < 1$), and $p(0) = 0$, $p(1) = c neq 0$. Let $f(x) = p(x) - cx$. Then $f(0) = f(1) = 0$ and $f(x + alpha) - f(x) = -calpha neq 0$ for all $x in [0, 1-alpha]$.
            – David Hartley
            Nov 17 at 2:14




            But f is only defined for $[0,1]$, your proof is incomplete until you show that the zero of g is in $[0, 1-1/n]$. Moreover, if you use an $alpha$ other than some $1/n$ the claim is false (even if $alpha$ is rational). Let p be a periodic function whose period is such an $alpha$, ($0 < alpha < 1$), and $p(0) = 0$, $p(1) = c neq 0$. Let $f(x) = p(x) - cx$. Then $f(0) = f(1) = 0$ and $f(x + alpha) - f(x) = -calpha neq 0$ for all $x in [0, 1-alpha]$.
            – David Hartley
            Nov 17 at 2:14


















             

            draft saved


            draft discarded



















































             


            draft saved


            draft discarded














            StackExchange.ready(
            function () {
            StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3000603%2flet-f-mathbbi-to-mathbbr-continuous-function-such-that-f0-f1%23new-answer', 'question_page');
            }
            );

            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







            Popular posts from this blog

            Probability when a professor distributes a quiz and homework assignment to a class of n students.

            Aardman Animations

            Are they similar matrix