Find the general term of $x_n+1 = fracx_n + 1n+1$ where $x_1 = 0$

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Find the general term of $x_n+1 = fracx_n + 1n + 1$ where $x_1 = 0$




I've tried finding the general term by introducing a generating function $G(z)$ and then solving for $G(z)$ with no luck.



I've also tried to express $x_n$ and get rid of the constant doing the following:



$$
x_n+1 = fracx_n + 1n+1\
x_n = fracx_n-1 + 1n
$$



Subtract one from another:



$$
(n+1)cdot x_n+1 - ncdot x_n = x_n - x_n-1
$$



So:
$$
(n+1)cdot (x_n+1 - x_n) = -x_n-1
$$



Not sure how to proceed from here. I've seen how recurrence relations are solve with characteristic equations. Should i introduce some characteristic polynomial and solve it?



Basically i'm more interested in a common approach than in solution (yet an example would be nice) since i am going to solve lots of similar problems after this one.







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    up vote
    3
    down vote

    favorite













    Find the general term of $x_n+1 = fracx_n + 1n + 1$ where $x_1 = 0$




    I've tried finding the general term by introducing a generating function $G(z)$ and then solving for $G(z)$ with no luck.



    I've also tried to express $x_n$ and get rid of the constant doing the following:



    $$
    x_n+1 = fracx_n + 1n+1\
    x_n = fracx_n-1 + 1n
    $$



    Subtract one from another:



    $$
    (n+1)cdot x_n+1 - ncdot x_n = x_n - x_n-1
    $$



    So:
    $$
    (n+1)cdot (x_n+1 - x_n) = -x_n-1
    $$



    Not sure how to proceed from here. I've seen how recurrence relations are solve with characteristic equations. Should i introduce some characteristic polynomial and solve it?



    Basically i'm more interested in a common approach than in solution (yet an example would be nice) since i am going to solve lots of similar problems after this one.







    share|cite|improve this question






















      up vote
      3
      down vote

      favorite









      up vote
      3
      down vote

      favorite












      Find the general term of $x_n+1 = fracx_n + 1n + 1$ where $x_1 = 0$




      I've tried finding the general term by introducing a generating function $G(z)$ and then solving for $G(z)$ with no luck.



      I've also tried to express $x_n$ and get rid of the constant doing the following:



      $$
      x_n+1 = fracx_n + 1n+1\
      x_n = fracx_n-1 + 1n
      $$



      Subtract one from another:



      $$
      (n+1)cdot x_n+1 - ncdot x_n = x_n - x_n-1
      $$



      So:
      $$
      (n+1)cdot (x_n+1 - x_n) = -x_n-1
      $$



      Not sure how to proceed from here. I've seen how recurrence relations are solve with characteristic equations. Should i introduce some characteristic polynomial and solve it?



      Basically i'm more interested in a common approach than in solution (yet an example would be nice) since i am going to solve lots of similar problems after this one.







      share|cite|improve this question













      Find the general term of $x_n+1 = fracx_n + 1n + 1$ where $x_1 = 0$




      I've tried finding the general term by introducing a generating function $G(z)$ and then solving for $G(z)$ with no luck.



      I've also tried to express $x_n$ and get rid of the constant doing the following:



      $$
      x_n+1 = fracx_n + 1n+1\
      x_n = fracx_n-1 + 1n
      $$



      Subtract one from another:



      $$
      (n+1)cdot x_n+1 - ncdot x_n = x_n - x_n-1
      $$



      So:
      $$
      (n+1)cdot (x_n+1 - x_n) = -x_n-1
      $$



      Not sure how to proceed from here. I've seen how recurrence relations are solve with characteristic equations. Should i introduce some characteristic polynomial and solve it?



      Basically i'm more interested in a common approach than in solution (yet an example would be nice) since i am going to solve lots of similar problems after this one.









      share|cite|improve this question











      share|cite|improve this question




      share|cite|improve this question










      asked Aug 10 at 16:19









      roman

      4391413




      4391413




















          2 Answers
          2






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          up vote
          5
          down vote



          accepted










          Hint. Let $z_n=n!x_n$ then $z_0=0$ and
          $$z_n+1=(n+1)!x_n+1=n!(n+1)x_n+1=n!(x_n+1)=z_n+n!\=
          z_n-1+(n-1)!+n!=sum_k=1^n k!$$






          share|cite|improve this answer






















          • Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
            – roman
            Aug 10 at 16:42







          • 2




            It's already linear. You were trying to transform it to a constant-coefficient recurrence.
            – Robert Israel
            Aug 10 at 17:03






          • 1




            @roman I was trying to transform the non-constant coefficient (linear) recurrence into a constant-coefficient one.
            – Robert Z
            Aug 10 at 17:05










          • @RobertIsrael Of course you are right. Thanks, for pointing out!!
            – Robert Z
            Aug 10 at 17:06

















          up vote
          1
          down vote













          Another way to find the same answer : let $x_n=fraca_nb_n$ (with $a_n$ and $b_n$ integers), then
          $$x_n+1=frac1+fraca_nb_nn+1=fraca_n+b_n(n+1)b_n$$
          so that
          $$a_n+1=a_n+b_ntext and b_n+1=(n+1)b_n$$
          with initial conditions $a_1=0$ and $b_1=1$.
          Solving this, you find $b_n=n!$, and $a_n=sum_k=1^n-1k!$, so
          $$x_n=frac1!+2!+dots+(n-1)!n!$$






          share|cite|improve this answer




















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            2 Answers
            2






            active

            oldest

            votes








            2 Answers
            2






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes








            up vote
            5
            down vote



            accepted










            Hint. Let $z_n=n!x_n$ then $z_0=0$ and
            $$z_n+1=(n+1)!x_n+1=n!(n+1)x_n+1=n!(x_n+1)=z_n+n!\=
            z_n-1+(n-1)!+n!=sum_k=1^n k!$$






            share|cite|improve this answer






















            • Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
              – roman
              Aug 10 at 16:42







            • 2




              It's already linear. You were trying to transform it to a constant-coefficient recurrence.
              – Robert Israel
              Aug 10 at 17:03






            • 1




              @roman I was trying to transform the non-constant coefficient (linear) recurrence into a constant-coefficient one.
              – Robert Z
              Aug 10 at 17:05










            • @RobertIsrael Of course you are right. Thanks, for pointing out!!
              – Robert Z
              Aug 10 at 17:06














            up vote
            5
            down vote



            accepted










            Hint. Let $z_n=n!x_n$ then $z_0=0$ and
            $$z_n+1=(n+1)!x_n+1=n!(n+1)x_n+1=n!(x_n+1)=z_n+n!\=
            z_n-1+(n-1)!+n!=sum_k=1^n k!$$






            share|cite|improve this answer






















            • Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
              – roman
              Aug 10 at 16:42







            • 2




              It's already linear. You were trying to transform it to a constant-coefficient recurrence.
              – Robert Israel
              Aug 10 at 17:03






            • 1




              @roman I was trying to transform the non-constant coefficient (linear) recurrence into a constant-coefficient one.
              – Robert Z
              Aug 10 at 17:05










            • @RobertIsrael Of course you are right. Thanks, for pointing out!!
              – Robert Z
              Aug 10 at 17:06












            up vote
            5
            down vote



            accepted







            up vote
            5
            down vote



            accepted






            Hint. Let $z_n=n!x_n$ then $z_0=0$ and
            $$z_n+1=(n+1)!x_n+1=n!(n+1)x_n+1=n!(x_n+1)=z_n+n!\=
            z_n-1+(n-1)!+n!=sum_k=1^n k!$$






            share|cite|improve this answer














            Hint. Let $z_n=n!x_n$ then $z_0=0$ and
            $$z_n+1=(n+1)!x_n+1=n!(n+1)x_n+1=n!(x_n+1)=z_n+n!\=
            z_n-1+(n-1)!+n!=sum_k=1^n k!$$







            share|cite|improve this answer














            share|cite|improve this answer



            share|cite|improve this answer








            edited Aug 10 at 16:39

























            answered Aug 10 at 16:32









            Robert Z

            84.2k955123




            84.2k955123











            • Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
              – roman
              Aug 10 at 16:42







            • 2




              It's already linear. You were trying to transform it to a constant-coefficient recurrence.
              – Robert Israel
              Aug 10 at 17:03






            • 1




              @roman I was trying to transform the non-constant coefficient (linear) recurrence into a constant-coefficient one.
              – Robert Z
              Aug 10 at 17:05










            • @RobertIsrael Of course you are right. Thanks, for pointing out!!
              – Robert Z
              Aug 10 at 17:06
















            • Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
              – roman
              Aug 10 at 16:42







            • 2




              It's already linear. You were trying to transform it to a constant-coefficient recurrence.
              – Robert Israel
              Aug 10 at 17:03






            • 1




              @roman I was trying to transform the non-constant coefficient (linear) recurrence into a constant-coefficient one.
              – Robert Z
              Aug 10 at 17:05










            • @RobertIsrael Of course you are right. Thanks, for pointing out!!
              – Robert Z
              Aug 10 at 17:06















            Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
            – roman
            Aug 10 at 16:42





            Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
            – roman
            Aug 10 at 16:42





            2




            2




            It's already linear. You were trying to transform it to a constant-coefficient recurrence.
            – Robert Israel
            Aug 10 at 17:03




            It's already linear. You were trying to transform it to a constant-coefficient recurrence.
            – Robert Israel
            Aug 10 at 17:03




            1




            1




            @roman I was trying to transform the non-constant coefficient (linear) recurrence into a constant-coefficient one.
            – Robert Z
            Aug 10 at 17:05




            @roman I was trying to transform the non-constant coefficient (linear) recurrence into a constant-coefficient one.
            – Robert Z
            Aug 10 at 17:05












            @RobertIsrael Of course you are right. Thanks, for pointing out!!
            – Robert Z
            Aug 10 at 17:06




            @RobertIsrael Of course you are right. Thanks, for pointing out!!
            – Robert Z
            Aug 10 at 17:06










            up vote
            1
            down vote













            Another way to find the same answer : let $x_n=fraca_nb_n$ (with $a_n$ and $b_n$ integers), then
            $$x_n+1=frac1+fraca_nb_nn+1=fraca_n+b_n(n+1)b_n$$
            so that
            $$a_n+1=a_n+b_ntext and b_n+1=(n+1)b_n$$
            with initial conditions $a_1=0$ and $b_1=1$.
            Solving this, you find $b_n=n!$, and $a_n=sum_k=1^n-1k!$, so
            $$x_n=frac1!+2!+dots+(n-1)!n!$$






            share|cite|improve this answer
























              up vote
              1
              down vote













              Another way to find the same answer : let $x_n=fraca_nb_n$ (with $a_n$ and $b_n$ integers), then
              $$x_n+1=frac1+fraca_nb_nn+1=fraca_n+b_n(n+1)b_n$$
              so that
              $$a_n+1=a_n+b_ntext and b_n+1=(n+1)b_n$$
              with initial conditions $a_1=0$ and $b_1=1$.
              Solving this, you find $b_n=n!$, and $a_n=sum_k=1^n-1k!$, so
              $$x_n=frac1!+2!+dots+(n-1)!n!$$






              share|cite|improve this answer






















                up vote
                1
                down vote










                up vote
                1
                down vote









                Another way to find the same answer : let $x_n=fraca_nb_n$ (with $a_n$ and $b_n$ integers), then
                $$x_n+1=frac1+fraca_nb_nn+1=fraca_n+b_n(n+1)b_n$$
                so that
                $$a_n+1=a_n+b_ntext and b_n+1=(n+1)b_n$$
                with initial conditions $a_1=0$ and $b_1=1$.
                Solving this, you find $b_n=n!$, and $a_n=sum_k=1^n-1k!$, so
                $$x_n=frac1!+2!+dots+(n-1)!n!$$






                share|cite|improve this answer












                Another way to find the same answer : let $x_n=fraca_nb_n$ (with $a_n$ and $b_n$ integers), then
                $$x_n+1=frac1+fraca_nb_nn+1=fraca_n+b_n(n+1)b_n$$
                so that
                $$a_n+1=a_n+b_ntext and b_n+1=(n+1)b_n$$
                with initial conditions $a_1=0$ and $b_1=1$.
                Solving this, you find $b_n=n!$, and $a_n=sum_k=1^n-1k!$, so
                $$x_n=frac1!+2!+dots+(n-1)!n!$$







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered Aug 10 at 17:16









                Nicolas FRANCOIS

                3,3001415




                3,3001415






















                     

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