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Sequence $lim_ntoinfty(-1)^n fracsin (n)n^2$



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 23, 2019 at 00:00UTC (8:00pm US/Eastern)Using the Test for DivergenceShow by comparison that $sumlimits_n=1^infty sin(frac1n)$ diverges?Convergence tests $sum_n=1^infty fracsin(n)n$Determining whether $ displaystyle sum_n = 0^infty 4cos(2pi n)e^-3n $ divergesDoes $sum_n=1^inftyln(nsin(frac1n))$ converge?Does $sumlimits_n=1^inftysin(n)sinleft(fracpi2nright)$ converge?Convergence of $sum_n=1^inftyfrac1(3n+8)!$A Sequence converges or divergesDetermine whether $sum_n=1^infty frac2sqrtn+2 $ converges or diverges?Show if the series $sum _n=1^infty frac 39n+1$ converges or diverges.










0












$begingroup$


So I have this problem and I need some help on it.



$$lim_ntoinfty(-1)^n fracsin (n)n^2$$



So for this, I know that the sin value will always be between -1 < n < 1.



And the series only converges if the limit is equal to 0, otherwise, it diverges by Divergence Test.



The problem is that I am having trouble taking the limit of the function:
$$lim_ntoinftyfracsin(n)n^2$$



So if anyone has any suggestions on how I may accomplish this, that would be great.










share|cite|improve this question











$endgroup$











  • $begingroup$
    Actually, you don't have $-1 < n <1$ but rather $-1 le sin n le 1.$
    $endgroup$
    – CiaPan
    Apr 1 at 18:45










  • $begingroup$
    Ah, I see thanks for the clarification.
    $endgroup$
    – Christian Martinez
    Apr 1 at 18:48















0












$begingroup$


So I have this problem and I need some help on it.



$$lim_ntoinfty(-1)^n fracsin (n)n^2$$



So for this, I know that the sin value will always be between -1 < n < 1.



And the series only converges if the limit is equal to 0, otherwise, it diverges by Divergence Test.



The problem is that I am having trouble taking the limit of the function:
$$lim_ntoinftyfracsin(n)n^2$$



So if anyone has any suggestions on how I may accomplish this, that would be great.










share|cite|improve this question











$endgroup$











  • $begingroup$
    Actually, you don't have $-1 < n <1$ but rather $-1 le sin n le 1.$
    $endgroup$
    – CiaPan
    Apr 1 at 18:45










  • $begingroup$
    Ah, I see thanks for the clarification.
    $endgroup$
    – Christian Martinez
    Apr 1 at 18:48













0












0








0





$begingroup$


So I have this problem and I need some help on it.



$$lim_ntoinfty(-1)^n fracsin (n)n^2$$



So for this, I know that the sin value will always be between -1 < n < 1.



And the series only converges if the limit is equal to 0, otherwise, it diverges by Divergence Test.



The problem is that I am having trouble taking the limit of the function:
$$lim_ntoinftyfracsin(n)n^2$$



So if anyone has any suggestions on how I may accomplish this, that would be great.










share|cite|improve this question











$endgroup$




So I have this problem and I need some help on it.



$$lim_ntoinfty(-1)^n fracsin (n)n^2$$



So for this, I know that the sin value will always be between -1 < n < 1.



And the series only converges if the limit is equal to 0, otherwise, it diverges by Divergence Test.



The problem is that I am having trouble taking the limit of the function:
$$lim_ntoinftyfracsin(n)n^2$$



So if anyone has any suggestions on how I may accomplish this, that would be great.







sequences-and-series






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Apr 1 at 18:39









Bernard

124k742117




124k742117










asked Apr 1 at 18:37









Christian MartinezChristian Martinez

648




648











  • $begingroup$
    Actually, you don't have $-1 < n <1$ but rather $-1 le sin n le 1.$
    $endgroup$
    – CiaPan
    Apr 1 at 18:45










  • $begingroup$
    Ah, I see thanks for the clarification.
    $endgroup$
    – Christian Martinez
    Apr 1 at 18:48
















  • $begingroup$
    Actually, you don't have $-1 < n <1$ but rather $-1 le sin n le 1.$
    $endgroup$
    – CiaPan
    Apr 1 at 18:45










  • $begingroup$
    Ah, I see thanks for the clarification.
    $endgroup$
    – Christian Martinez
    Apr 1 at 18:48















$begingroup$
Actually, you don't have $-1 < n <1$ but rather $-1 le sin n le 1.$
$endgroup$
– CiaPan
Apr 1 at 18:45




$begingroup$
Actually, you don't have $-1 < n <1$ but rather $-1 le sin n le 1.$
$endgroup$
– CiaPan
Apr 1 at 18:45












$begingroup$
Ah, I see thanks for the clarification.
$endgroup$
– Christian Martinez
Apr 1 at 18:48




$begingroup$
Ah, I see thanks for the clarification.
$endgroup$
– Christian Martinez
Apr 1 at 18:48










3 Answers
3






active

oldest

votes


















4












$begingroup$

Guide:



  • Note that

$$left|fracsin nn^2right| le frac1n^2$$






share|cite|improve this answer









$endgroup$








  • 1




    $begingroup$
    So would I take the limit of $$frac1n^2$$ which is 0. So then the sequence converges -- this is squeeze theorem right?
    $endgroup$
    – Christian Martinez
    Apr 1 at 18:41







  • 1




    $begingroup$
    yup, after you show that the absolute value of $|a_n|$ converges to $0$, you can conclude that $a_n$ converges to $0$ as well. Alternatively, view it as $-frac1n^2 le fracsin nn^2 le frac1n^2$.
    $endgroup$
    – Siong Thye Goh
    Apr 1 at 18:42







  • 1




    $begingroup$
    Alright, thanks!
    $endgroup$
    – Christian Martinez
    Apr 1 at 18:43


















4












$begingroup$

We need to observe that $$frac-1n^2 leq frac(-1)^nsin(n)n^2 leq frac1n^2$$



Since $lim_n to infty frac-1n^2 = lim_n to infty frac1n^2 = 0$, it follows by the squeeze theorem that
$$lim_n to infty frac(-1)^nsin(n)n^2 = 0$$






share|cite|improve this answer









$endgroup$




















    0












    $begingroup$

    If you know that for some positive $M$, $-Mleq f(x)leq M$ for all $x$, then $-Mleq lim_xrightarrowinftyf(x)leq M$.



    Now use the fact that $-1 leq (-1)^nsin(n)leq 1$ and $lim_nrightarrowinftyfrac 1 n^2=0$ to conclude that the answer to your question is zero.






    share|cite|improve this answer









    $endgroup$













      Your Answer








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      3 Answers
      3






      active

      oldest

      votes








      3 Answers
      3






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      4












      $begingroup$

      Guide:



      • Note that

      $$left|fracsin nn^2right| le frac1n^2$$






      share|cite|improve this answer









      $endgroup$








      • 1




        $begingroup$
        So would I take the limit of $$frac1n^2$$ which is 0. So then the sequence converges -- this is squeeze theorem right?
        $endgroup$
        – Christian Martinez
        Apr 1 at 18:41







      • 1




        $begingroup$
        yup, after you show that the absolute value of $|a_n|$ converges to $0$, you can conclude that $a_n$ converges to $0$ as well. Alternatively, view it as $-frac1n^2 le fracsin nn^2 le frac1n^2$.
        $endgroup$
        – Siong Thye Goh
        Apr 1 at 18:42







      • 1




        $begingroup$
        Alright, thanks!
        $endgroup$
        – Christian Martinez
        Apr 1 at 18:43















      4












      $begingroup$

      Guide:



      • Note that

      $$left|fracsin nn^2right| le frac1n^2$$






      share|cite|improve this answer









      $endgroup$








      • 1




        $begingroup$
        So would I take the limit of $$frac1n^2$$ which is 0. So then the sequence converges -- this is squeeze theorem right?
        $endgroup$
        – Christian Martinez
        Apr 1 at 18:41







      • 1




        $begingroup$
        yup, after you show that the absolute value of $|a_n|$ converges to $0$, you can conclude that $a_n$ converges to $0$ as well. Alternatively, view it as $-frac1n^2 le fracsin nn^2 le frac1n^2$.
        $endgroup$
        – Siong Thye Goh
        Apr 1 at 18:42







      • 1




        $begingroup$
        Alright, thanks!
        $endgroup$
        – Christian Martinez
        Apr 1 at 18:43













      4












      4








      4





      $begingroup$

      Guide:



      • Note that

      $$left|fracsin nn^2right| le frac1n^2$$






      share|cite|improve this answer









      $endgroup$



      Guide:



      • Note that

      $$left|fracsin nn^2right| le frac1n^2$$







      share|cite|improve this answer












      share|cite|improve this answer



      share|cite|improve this answer










      answered Apr 1 at 18:39









      Siong Thye GohSiong Thye Goh

      104k1468120




      104k1468120







      • 1




        $begingroup$
        So would I take the limit of $$frac1n^2$$ which is 0. So then the sequence converges -- this is squeeze theorem right?
        $endgroup$
        – Christian Martinez
        Apr 1 at 18:41







      • 1




        $begingroup$
        yup, after you show that the absolute value of $|a_n|$ converges to $0$, you can conclude that $a_n$ converges to $0$ as well. Alternatively, view it as $-frac1n^2 le fracsin nn^2 le frac1n^2$.
        $endgroup$
        – Siong Thye Goh
        Apr 1 at 18:42







      • 1




        $begingroup$
        Alright, thanks!
        $endgroup$
        – Christian Martinez
        Apr 1 at 18:43












      • 1




        $begingroup$
        So would I take the limit of $$frac1n^2$$ which is 0. So then the sequence converges -- this is squeeze theorem right?
        $endgroup$
        – Christian Martinez
        Apr 1 at 18:41







      • 1




        $begingroup$
        yup, after you show that the absolute value of $|a_n|$ converges to $0$, you can conclude that $a_n$ converges to $0$ as well. Alternatively, view it as $-frac1n^2 le fracsin nn^2 le frac1n^2$.
        $endgroup$
        – Siong Thye Goh
        Apr 1 at 18:42







      • 1




        $begingroup$
        Alright, thanks!
        $endgroup$
        – Christian Martinez
        Apr 1 at 18:43







      1




      1




      $begingroup$
      So would I take the limit of $$frac1n^2$$ which is 0. So then the sequence converges -- this is squeeze theorem right?
      $endgroup$
      – Christian Martinez
      Apr 1 at 18:41





      $begingroup$
      So would I take the limit of $$frac1n^2$$ which is 0. So then the sequence converges -- this is squeeze theorem right?
      $endgroup$
      – Christian Martinez
      Apr 1 at 18:41





      1




      1




      $begingroup$
      yup, after you show that the absolute value of $|a_n|$ converges to $0$, you can conclude that $a_n$ converges to $0$ as well. Alternatively, view it as $-frac1n^2 le fracsin nn^2 le frac1n^2$.
      $endgroup$
      – Siong Thye Goh
      Apr 1 at 18:42





      $begingroup$
      yup, after you show that the absolute value of $|a_n|$ converges to $0$, you can conclude that $a_n$ converges to $0$ as well. Alternatively, view it as $-frac1n^2 le fracsin nn^2 le frac1n^2$.
      $endgroup$
      – Siong Thye Goh
      Apr 1 at 18:42





      1




      1




      $begingroup$
      Alright, thanks!
      $endgroup$
      – Christian Martinez
      Apr 1 at 18:43




      $begingroup$
      Alright, thanks!
      $endgroup$
      – Christian Martinez
      Apr 1 at 18:43











      4












      $begingroup$

      We need to observe that $$frac-1n^2 leq frac(-1)^nsin(n)n^2 leq frac1n^2$$



      Since $lim_n to infty frac-1n^2 = lim_n to infty frac1n^2 = 0$, it follows by the squeeze theorem that
      $$lim_n to infty frac(-1)^nsin(n)n^2 = 0$$






      share|cite|improve this answer









      $endgroup$

















        4












        $begingroup$

        We need to observe that $$frac-1n^2 leq frac(-1)^nsin(n)n^2 leq frac1n^2$$



        Since $lim_n to infty frac-1n^2 = lim_n to infty frac1n^2 = 0$, it follows by the squeeze theorem that
        $$lim_n to infty frac(-1)^nsin(n)n^2 = 0$$






        share|cite|improve this answer









        $endgroup$















          4












          4








          4





          $begingroup$

          We need to observe that $$frac-1n^2 leq frac(-1)^nsin(n)n^2 leq frac1n^2$$



          Since $lim_n to infty frac-1n^2 = lim_n to infty frac1n^2 = 0$, it follows by the squeeze theorem that
          $$lim_n to infty frac(-1)^nsin(n)n^2 = 0$$






          share|cite|improve this answer









          $endgroup$



          We need to observe that $$frac-1n^2 leq frac(-1)^nsin(n)n^2 leq frac1n^2$$



          Since $lim_n to infty frac-1n^2 = lim_n to infty frac1n^2 = 0$, it follows by the squeeze theorem that
          $$lim_n to infty frac(-1)^nsin(n)n^2 = 0$$







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Apr 1 at 18:43









          user516079user516079

          537311




          537311





















              0












              $begingroup$

              If you know that for some positive $M$, $-Mleq f(x)leq M$ for all $x$, then $-Mleq lim_xrightarrowinftyf(x)leq M$.



              Now use the fact that $-1 leq (-1)^nsin(n)leq 1$ and $lim_nrightarrowinftyfrac 1 n^2=0$ to conclude that the answer to your question is zero.






              share|cite|improve this answer









              $endgroup$

















                0












                $begingroup$

                If you know that for some positive $M$, $-Mleq f(x)leq M$ for all $x$, then $-Mleq lim_xrightarrowinftyf(x)leq M$.



                Now use the fact that $-1 leq (-1)^nsin(n)leq 1$ and $lim_nrightarrowinftyfrac 1 n^2=0$ to conclude that the answer to your question is zero.






                share|cite|improve this answer









                $endgroup$















                  0












                  0








                  0





                  $begingroup$

                  If you know that for some positive $M$, $-Mleq f(x)leq M$ for all $x$, then $-Mleq lim_xrightarrowinftyf(x)leq M$.



                  Now use the fact that $-1 leq (-1)^nsin(n)leq 1$ and $lim_nrightarrowinftyfrac 1 n^2=0$ to conclude that the answer to your question is zero.






                  share|cite|improve this answer









                  $endgroup$



                  If you know that for some positive $M$, $-Mleq f(x)leq M$ for all $x$, then $-Mleq lim_xrightarrowinftyf(x)leq M$.



                  Now use the fact that $-1 leq (-1)^nsin(n)leq 1$ and $lim_nrightarrowinftyfrac 1 n^2=0$ to conclude that the answer to your question is zero.







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered Apr 1 at 18:48









                  zornzorn

                  516




                  516



























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