How can I claim a one-sided limit doesn't exist?












4












$begingroup$


I have to find the limit $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}} $$



Now, I tried using L'Hôpital's rule, but it doesn't lead anywhere.



Manually trying to convert the functions to another form doesn't seem to go anywhere either, so I determined that the limit must be undefined.



However, I cannot prove it. What can I do?










share|cite|improve this question











$endgroup$








  • 2




    $begingroup$
    Using Taylor, the numerator is $2xcdot x+o(x^3)$ and the limit is $0$.
    $endgroup$
    – Yves Daoust
    Jan 30 at 16:37










  • $begingroup$
    We haven't been taught about Taylor yet, I should add this to my question. However, thanks for the answer, i'll research Taylor on my own.
    $endgroup$
    – sdds
    Jan 30 at 16:40












  • $begingroup$
    To answer the question in the title, see for example here
    $endgroup$
    – BlueRaja - Danny Pflughoeft
    Jan 30 at 21:37










  • $begingroup$
    After you ask a question here, if you get an acceptable answer, you should "accept" the answer by clicking the check mark $checkmark$ next to it. This scores points for you and for the person who answered your question. You can find out more about accepting answers here: How do I accept an answer?, Why should we accept answers?, What should I do if someone answers my question?.
    $endgroup$
    – Clement C.
    Feb 3 at 23:26
















4












$begingroup$


I have to find the limit $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}} $$



Now, I tried using L'Hôpital's rule, but it doesn't lead anywhere.



Manually trying to convert the functions to another form doesn't seem to go anywhere either, so I determined that the limit must be undefined.



However, I cannot prove it. What can I do?










share|cite|improve this question











$endgroup$








  • 2




    $begingroup$
    Using Taylor, the numerator is $2xcdot x+o(x^3)$ and the limit is $0$.
    $endgroup$
    – Yves Daoust
    Jan 30 at 16:37










  • $begingroup$
    We haven't been taught about Taylor yet, I should add this to my question. However, thanks for the answer, i'll research Taylor on my own.
    $endgroup$
    – sdds
    Jan 30 at 16:40












  • $begingroup$
    To answer the question in the title, see for example here
    $endgroup$
    – BlueRaja - Danny Pflughoeft
    Jan 30 at 21:37










  • $begingroup$
    After you ask a question here, if you get an acceptable answer, you should "accept" the answer by clicking the check mark $checkmark$ next to it. This scores points for you and for the person who answered your question. You can find out more about accepting answers here: How do I accept an answer?, Why should we accept answers?, What should I do if someone answers my question?.
    $endgroup$
    – Clement C.
    Feb 3 at 23:26














4












4








4





$begingroup$


I have to find the limit $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}} $$



Now, I tried using L'Hôpital's rule, but it doesn't lead anywhere.



Manually trying to convert the functions to another form doesn't seem to go anywhere either, so I determined that the limit must be undefined.



However, I cannot prove it. What can I do?










share|cite|improve this question











$endgroup$




I have to find the limit $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}} $$



Now, I tried using L'Hôpital's rule, but it doesn't lead anywhere.



Manually trying to convert the functions to another form doesn't seem to go anywhere either, so I determined that the limit must be undefined.



However, I cannot prove it. What can I do?







real-analysis limits logarithms proof-explanation limits-without-lhopital






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Feb 28 at 7:46









Michael Rozenberg

109k1896201




109k1896201










asked Jan 30 at 16:21









sddssdds

296




296








  • 2




    $begingroup$
    Using Taylor, the numerator is $2xcdot x+o(x^3)$ and the limit is $0$.
    $endgroup$
    – Yves Daoust
    Jan 30 at 16:37










  • $begingroup$
    We haven't been taught about Taylor yet, I should add this to my question. However, thanks for the answer, i'll research Taylor on my own.
    $endgroup$
    – sdds
    Jan 30 at 16:40












  • $begingroup$
    To answer the question in the title, see for example here
    $endgroup$
    – BlueRaja - Danny Pflughoeft
    Jan 30 at 21:37










  • $begingroup$
    After you ask a question here, if you get an acceptable answer, you should "accept" the answer by clicking the check mark $checkmark$ next to it. This scores points for you and for the person who answered your question. You can find out more about accepting answers here: How do I accept an answer?, Why should we accept answers?, What should I do if someone answers my question?.
    $endgroup$
    – Clement C.
    Feb 3 at 23:26














  • 2




    $begingroup$
    Using Taylor, the numerator is $2xcdot x+o(x^3)$ and the limit is $0$.
    $endgroup$
    – Yves Daoust
    Jan 30 at 16:37










  • $begingroup$
    We haven't been taught about Taylor yet, I should add this to my question. However, thanks for the answer, i'll research Taylor on my own.
    $endgroup$
    – sdds
    Jan 30 at 16:40












  • $begingroup$
    To answer the question in the title, see for example here
    $endgroup$
    – BlueRaja - Danny Pflughoeft
    Jan 30 at 21:37










  • $begingroup$
    After you ask a question here, if you get an acceptable answer, you should "accept" the answer by clicking the check mark $checkmark$ next to it. This scores points for you and for the person who answered your question. You can find out more about accepting answers here: How do I accept an answer?, Why should we accept answers?, What should I do if someone answers my question?.
    $endgroup$
    – Clement C.
    Feb 3 at 23:26








2




2




$begingroup$
Using Taylor, the numerator is $2xcdot x+o(x^3)$ and the limit is $0$.
$endgroup$
– Yves Daoust
Jan 30 at 16:37




$begingroup$
Using Taylor, the numerator is $2xcdot x+o(x^3)$ and the limit is $0$.
$endgroup$
– Yves Daoust
Jan 30 at 16:37












$begingroup$
We haven't been taught about Taylor yet, I should add this to my question. However, thanks for the answer, i'll research Taylor on my own.
$endgroup$
– sdds
Jan 30 at 16:40






$begingroup$
We haven't been taught about Taylor yet, I should add this to my question. However, thanks for the answer, i'll research Taylor on my own.
$endgroup$
– sdds
Jan 30 at 16:40














$begingroup$
To answer the question in the title, see for example here
$endgroup$
– BlueRaja - Danny Pflughoeft
Jan 30 at 21:37




$begingroup$
To answer the question in the title, see for example here
$endgroup$
– BlueRaja - Danny Pflughoeft
Jan 30 at 21:37












$begingroup$
After you ask a question here, if you get an acceptable answer, you should "accept" the answer by clicking the check mark $checkmark$ next to it. This scores points for you and for the person who answered your question. You can find out more about accepting answers here: How do I accept an answer?, Why should we accept answers?, What should I do if someone answers my question?.
$endgroup$
– Clement C.
Feb 3 at 23:26




$begingroup$
After you ask a question here, if you get an acceptable answer, you should "accept" the answer by clicking the check mark $checkmark$ next to it. This scores points for you and for the person who answered your question. You can find out more about accepting answers here: How do I accept an answer?, Why should we accept answers?, What should I do if someone answers my question?.
$endgroup$
– Clement C.
Feb 3 at 23:26










4 Answers
4






active

oldest

votes


















13












$begingroup$

Hint:



Use the facts that (1) $lim_{xto 0} frac{ln(1+2x)}{2x} = 1$, (2) $lim_{xto 0} frac{sin x}{x} = 1$, and (3) $lim_{xto 0^+} frac{x^2}{sqrt{x^3}} = 0$ to show the limit is $2cdot 1cdot 0 = 0$.



To do so, rewrite, for $x>0$,
$$
frac{ln(1+2x)sin x}{sqrt{x^3}}=2cdot frac{ln(1+2x)}{2x}cdotfrac{sin x}{x}cdotfrac{x^2}{sqrt{x^3}}
$$






share|cite|improve this answer









$endgroup$













  • $begingroup$
    Thank you, this conversion never occurred to me
    $endgroup$
    – sdds
    Jan 30 at 16:37










  • $begingroup$
    @sdds You're welcome!
    $endgroup$
    – Clement C.
    Jan 30 at 16:40



















11












$begingroup$

$$frac{ln(1+2x)sin{x}}{sqrt{x^3}}=frac{ln(1+2x)}{2x}cdotfrac{sin{x}}{x}cdot2sqrt{x}rightarrow0.$$






share|cite|improve this answer









$endgroup$





















    3












    $begingroup$

    It is known that



    $$lim_{xto 0^+}frac{sin x}x=1$$ and $$lim_{xto 0^+}frac{log(1+x)}x=1=lim_{xto 0^+}frac{log(1+2x)}{2x}.$$



    Then



    $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}}=1cdot2cdotlim_{xto 0^+} sqrt x.$$






    share|cite|improve this answer









    $endgroup$









    • 2




      $begingroup$
      It's true, but how is that different from the current two answers?
      $endgroup$
      – Clement C.
      Jan 30 at 16:45



















    0












    $begingroup$

    If you want to, you should apply L'Hospital's rule twice:
    $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}}=\
    lim_{xto 0^+} frac{frac{2}{1+2x}sin x+ln(1+2x)cos x}{1.5sqrt {x}}=\
    lim_{xto 0^+} frac{frac{-4}{(1+2x)^2}sin x+frac{2}{1+2x}cos x+frac{2}{1+2x}cos x-ln(1+2x)sin x}{frac{0.75}{sqrt {x}}}=0.
    $$






    share|cite|improve this answer









    $endgroup$














      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
      });


      }
      });














      draft saved

      draft discarded


















      StackExchange.ready(
      function () {
      StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3093744%2fhow-can-i-claim-a-one-sided-limit-doesnt-exist%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









      13












      $begingroup$

      Hint:



      Use the facts that (1) $lim_{xto 0} frac{ln(1+2x)}{2x} = 1$, (2) $lim_{xto 0} frac{sin x}{x} = 1$, and (3) $lim_{xto 0^+} frac{x^2}{sqrt{x^3}} = 0$ to show the limit is $2cdot 1cdot 0 = 0$.



      To do so, rewrite, for $x>0$,
      $$
      frac{ln(1+2x)sin x}{sqrt{x^3}}=2cdot frac{ln(1+2x)}{2x}cdotfrac{sin x}{x}cdotfrac{x^2}{sqrt{x^3}}
      $$






      share|cite|improve this answer









      $endgroup$













      • $begingroup$
        Thank you, this conversion never occurred to me
        $endgroup$
        – sdds
        Jan 30 at 16:37










      • $begingroup$
        @sdds You're welcome!
        $endgroup$
        – Clement C.
        Jan 30 at 16:40
















      13












      $begingroup$

      Hint:



      Use the facts that (1) $lim_{xto 0} frac{ln(1+2x)}{2x} = 1$, (2) $lim_{xto 0} frac{sin x}{x} = 1$, and (3) $lim_{xto 0^+} frac{x^2}{sqrt{x^3}} = 0$ to show the limit is $2cdot 1cdot 0 = 0$.



      To do so, rewrite, for $x>0$,
      $$
      frac{ln(1+2x)sin x}{sqrt{x^3}}=2cdot frac{ln(1+2x)}{2x}cdotfrac{sin x}{x}cdotfrac{x^2}{sqrt{x^3}}
      $$






      share|cite|improve this answer









      $endgroup$













      • $begingroup$
        Thank you, this conversion never occurred to me
        $endgroup$
        – sdds
        Jan 30 at 16:37










      • $begingroup$
        @sdds You're welcome!
        $endgroup$
        – Clement C.
        Jan 30 at 16:40














      13












      13








      13





      $begingroup$

      Hint:



      Use the facts that (1) $lim_{xto 0} frac{ln(1+2x)}{2x} = 1$, (2) $lim_{xto 0} frac{sin x}{x} = 1$, and (3) $lim_{xto 0^+} frac{x^2}{sqrt{x^3}} = 0$ to show the limit is $2cdot 1cdot 0 = 0$.



      To do so, rewrite, for $x>0$,
      $$
      frac{ln(1+2x)sin x}{sqrt{x^3}}=2cdot frac{ln(1+2x)}{2x}cdotfrac{sin x}{x}cdotfrac{x^2}{sqrt{x^3}}
      $$






      share|cite|improve this answer









      $endgroup$



      Hint:



      Use the facts that (1) $lim_{xto 0} frac{ln(1+2x)}{2x} = 1$, (2) $lim_{xto 0} frac{sin x}{x} = 1$, and (3) $lim_{xto 0^+} frac{x^2}{sqrt{x^3}} = 0$ to show the limit is $2cdot 1cdot 0 = 0$.



      To do so, rewrite, for $x>0$,
      $$
      frac{ln(1+2x)sin x}{sqrt{x^3}}=2cdot frac{ln(1+2x)}{2x}cdotfrac{sin x}{x}cdotfrac{x^2}{sqrt{x^3}}
      $$







      share|cite|improve this answer












      share|cite|improve this answer



      share|cite|improve this answer










      answered Jan 30 at 16:24









      Clement C.Clement C.

      51k34093




      51k34093












      • $begingroup$
        Thank you, this conversion never occurred to me
        $endgroup$
        – sdds
        Jan 30 at 16:37










      • $begingroup$
        @sdds You're welcome!
        $endgroup$
        – Clement C.
        Jan 30 at 16:40


















      • $begingroup$
        Thank you, this conversion never occurred to me
        $endgroup$
        – sdds
        Jan 30 at 16:37










      • $begingroup$
        @sdds You're welcome!
        $endgroup$
        – Clement C.
        Jan 30 at 16:40
















      $begingroup$
      Thank you, this conversion never occurred to me
      $endgroup$
      – sdds
      Jan 30 at 16:37




      $begingroup$
      Thank you, this conversion never occurred to me
      $endgroup$
      – sdds
      Jan 30 at 16:37












      $begingroup$
      @sdds You're welcome!
      $endgroup$
      – Clement C.
      Jan 30 at 16:40




      $begingroup$
      @sdds You're welcome!
      $endgroup$
      – Clement C.
      Jan 30 at 16:40











      11












      $begingroup$

      $$frac{ln(1+2x)sin{x}}{sqrt{x^3}}=frac{ln(1+2x)}{2x}cdotfrac{sin{x}}{x}cdot2sqrt{x}rightarrow0.$$






      share|cite|improve this answer









      $endgroup$


















        11












        $begingroup$

        $$frac{ln(1+2x)sin{x}}{sqrt{x^3}}=frac{ln(1+2x)}{2x}cdotfrac{sin{x}}{x}cdot2sqrt{x}rightarrow0.$$






        share|cite|improve this answer









        $endgroup$
















          11












          11








          11





          $begingroup$

          $$frac{ln(1+2x)sin{x}}{sqrt{x^3}}=frac{ln(1+2x)}{2x}cdotfrac{sin{x}}{x}cdot2sqrt{x}rightarrow0.$$






          share|cite|improve this answer









          $endgroup$



          $$frac{ln(1+2x)sin{x}}{sqrt{x^3}}=frac{ln(1+2x)}{2x}cdotfrac{sin{x}}{x}cdot2sqrt{x}rightarrow0.$$







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Jan 30 at 16:24









          Michael RozenbergMichael Rozenberg

          109k1896201




          109k1896201























              3












              $begingroup$

              It is known that



              $$lim_{xto 0^+}frac{sin x}x=1$$ and $$lim_{xto 0^+}frac{log(1+x)}x=1=lim_{xto 0^+}frac{log(1+2x)}{2x}.$$



              Then



              $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}}=1cdot2cdotlim_{xto 0^+} sqrt x.$$






              share|cite|improve this answer









              $endgroup$









              • 2




                $begingroup$
                It's true, but how is that different from the current two answers?
                $endgroup$
                – Clement C.
                Jan 30 at 16:45
















              3












              $begingroup$

              It is known that



              $$lim_{xto 0^+}frac{sin x}x=1$$ and $$lim_{xto 0^+}frac{log(1+x)}x=1=lim_{xto 0^+}frac{log(1+2x)}{2x}.$$



              Then



              $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}}=1cdot2cdotlim_{xto 0^+} sqrt x.$$






              share|cite|improve this answer









              $endgroup$









              • 2




                $begingroup$
                It's true, but how is that different from the current two answers?
                $endgroup$
                – Clement C.
                Jan 30 at 16:45














              3












              3








              3





              $begingroup$

              It is known that



              $$lim_{xto 0^+}frac{sin x}x=1$$ and $$lim_{xto 0^+}frac{log(1+x)}x=1=lim_{xto 0^+}frac{log(1+2x)}{2x}.$$



              Then



              $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}}=1cdot2cdotlim_{xto 0^+} sqrt x.$$






              share|cite|improve this answer









              $endgroup$



              It is known that



              $$lim_{xto 0^+}frac{sin x}x=1$$ and $$lim_{xto 0^+}frac{log(1+x)}x=1=lim_{xto 0^+}frac{log(1+2x)}{2x}.$$



              Then



              $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}}=1cdot2cdotlim_{xto 0^+} sqrt x.$$







              share|cite|improve this answer












              share|cite|improve this answer



              share|cite|improve this answer










              answered Jan 30 at 16:42









              Yves DaoustYves Daoust

              132k676229




              132k676229








              • 2




                $begingroup$
                It's true, but how is that different from the current two answers?
                $endgroup$
                – Clement C.
                Jan 30 at 16:45














              • 2




                $begingroup$
                It's true, but how is that different from the current two answers?
                $endgroup$
                – Clement C.
                Jan 30 at 16:45








              2




              2




              $begingroup$
              It's true, but how is that different from the current two answers?
              $endgroup$
              – Clement C.
              Jan 30 at 16:45




              $begingroup$
              It's true, but how is that different from the current two answers?
              $endgroup$
              – Clement C.
              Jan 30 at 16:45











              0












              $begingroup$

              If you want to, you should apply L'Hospital's rule twice:
              $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}}=\
              lim_{xto 0^+} frac{frac{2}{1+2x}sin x+ln(1+2x)cos x}{1.5sqrt {x}}=\
              lim_{xto 0^+} frac{frac{-4}{(1+2x)^2}sin x+frac{2}{1+2x}cos x+frac{2}{1+2x}cos x-ln(1+2x)sin x}{frac{0.75}{sqrt {x}}}=0.
              $$






              share|cite|improve this answer









              $endgroup$


















                0












                $begingroup$

                If you want to, you should apply L'Hospital's rule twice:
                $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}}=\
                lim_{xto 0^+} frac{frac{2}{1+2x}sin x+ln(1+2x)cos x}{1.5sqrt {x}}=\
                lim_{xto 0^+} frac{frac{-4}{(1+2x)^2}sin x+frac{2}{1+2x}cos x+frac{2}{1+2x}cos x-ln(1+2x)sin x}{frac{0.75}{sqrt {x}}}=0.
                $$






                share|cite|improve this answer









                $endgroup$
















                  0












                  0








                  0





                  $begingroup$

                  If you want to, you should apply L'Hospital's rule twice:
                  $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}}=\
                  lim_{xto 0^+} frac{frac{2}{1+2x}sin x+ln(1+2x)cos x}{1.5sqrt {x}}=\
                  lim_{xto 0^+} frac{frac{-4}{(1+2x)^2}sin x+frac{2}{1+2x}cos x+frac{2}{1+2x}cos x-ln(1+2x)sin x}{frac{0.75}{sqrt {x}}}=0.
                  $$






                  share|cite|improve this answer









                  $endgroup$



                  If you want to, you should apply L'Hospital's rule twice:
                  $$lim_{xto 0^+} frac{ln(1+2x)sin x}{sqrt {x^3}}=\
                  lim_{xto 0^+} frac{frac{2}{1+2x}sin x+ln(1+2x)cos x}{1.5sqrt {x}}=\
                  lim_{xto 0^+} frac{frac{-4}{(1+2x)^2}sin x+frac{2}{1+2x}cos x+frac{2}{1+2x}cos x-ln(1+2x)sin x}{frac{0.75}{sqrt {x}}}=0.
                  $$







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered Feb 28 at 10:15









                  farruhotafarruhota

                  21.8k2842




                  21.8k2842






























                      draft saved

                      draft discarded




















































                      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.




                      draft saved


                      draft discarded














                      StackExchange.ready(
                      function () {
                      StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3093744%2fhow-can-i-claim-a-one-sided-limit-doesnt-exist%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

                      'app-layout' is not a known element: how to share Component with different Modules

                      android studio warns about leanback feature tag usage required on manifest while using Unity exported app?

                      WPF add header to Image with URL pettitions [duplicate]