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.
sequences-and-series algebra-precalculus
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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.
sequences-and-series algebra-precalculus
add a comment |Â
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.
sequences-and-series algebra-precalculus
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.
sequences-and-series algebra-precalculus
asked Aug 10 at 16:19
roman
4391413
4391413
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2 Answers
2
active
oldest
votes
up vote
5
down vote
accepted
Hint. Let $z_n=n!x_n$ then $z_0=0$ and
$$z_n+1=(n+1)!x_n+1=n!(n+1)x_n+1=n!(x_n+1)=z_n+n!\=
z_n-1+(n-1)!+n!=sum_k=1^n k!$$
Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
â roman
Aug 10 at 16:42
2
It's already linear. You were trying to transform it to a constant-coefficient recurrence.
â 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.
â Robert Z
Aug 10 at 17:05
@RobertIsrael Of course you are right. Thanks, for pointing out!!
â Robert Z
Aug 10 at 17:06
add a comment |Â
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
$$x_n=frac1!+2!+dots+(n-1)!n!$$
add a comment |Â
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
$$z_n+1=(n+1)!x_n+1=n!(n+1)x_n+1=n!(x_n+1)=z_n+n!\=
z_n-1+(n-1)!+n!=sum_k=1^n k!$$
Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
â roman
Aug 10 at 16:42
2
It's already linear. You were trying to transform it to a constant-coefficient recurrence.
â 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.
â Robert Z
Aug 10 at 17:05
@RobertIsrael Of course you are right. Thanks, for pointing out!!
â Robert Z
Aug 10 at 17:06
add a comment |Â
up vote
5
down vote
accepted
Hint. Let $z_n=n!x_n$ then $z_0=0$ and
$$z_n+1=(n+1)!x_n+1=n!(n+1)x_n+1=n!(x_n+1)=z_n+n!\=
z_n-1+(n-1)!+n!=sum_k=1^n k!$$
Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
â roman
Aug 10 at 16:42
2
It's already linear. You were trying to transform it to a constant-coefficient recurrence.
â 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.
â Robert Z
Aug 10 at 17:05
@RobertIsrael Of course you are right. Thanks, for pointing out!!
â Robert Z
Aug 10 at 17:06
add a comment |Â
up vote
5
down vote
accepted
up vote
5
down vote
accepted
Hint. Let $z_n=n!x_n$ then $z_0=0$ and
$$z_n+1=(n+1)!x_n+1=n!(n+1)x_n+1=n!(x_n+1)=z_n+n!\=
z_n-1+(n-1)!+n!=sum_k=1^n k!$$
Hint. Let $z_n=n!x_n$ then $z_0=0$ and
$$z_n+1=(n+1)!x_n+1=n!(n+1)x_n+1=n!(x_n+1)=z_n+n!\=
z_n-1+(n-1)!+n!=sum_k=1^n k!$$
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 $z_n = n!x_n$?
â roman
Aug 10 at 16:42
2
It's already linear. You were trying to transform it to a constant-coefficient recurrence.
â 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.
â Robert Z
Aug 10 at 17:05
@RobertIsrael Of course you are right. Thanks, for pointing out!!
â Robert Z
Aug 10 at 17:06
add a comment |Â
Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
â roman
Aug 10 at 16:42
2
It's already linear. You were trying to transform it to a constant-coefficient recurrence.
â 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.
â Robert Z
Aug 10 at 17:05
@RobertIsrael Of course you are right. Thanks, for pointing out!!
â 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 $z_n = n!x_n$?
â roman
Aug 10 at 16:42
Thank you for the answer. Could you please explain how you would come with an idea to introduce $z_n = n!x_n$?
â roman
Aug 10 at 16:42
2
2
It's already linear. You were trying to transform it to a constant-coefficient recurrence.
â Robert Israel
Aug 10 at 17:03
It's already linear. You were trying to transform it to a constant-coefficient recurrence.
â 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.
â Robert Z
Aug 10 at 17:05
@roman I was trying to transform the non-constant coefficient (linear) recurrence into a constant-coefficient one.
â Robert Z
Aug 10 at 17:05
@RobertIsrael Of course you are right. Thanks, for pointing out!!
â Robert Z
Aug 10 at 17:06
@RobertIsrael Of course you are right. Thanks, for pointing out!!
â Robert Z
Aug 10 at 17:06
add a comment |Â
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
$$x_n=frac1!+2!+dots+(n-1)!n!$$
add a comment |Â
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
$$x_n=frac1!+2!+dots+(n-1)!n!$$
add a comment |Â
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
$$x_n=frac1!+2!+dots+(n-1)!n!$$
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
$$x_n=frac1!+2!+dots+(n-1)!n!$$
answered Aug 10 at 17:16
Nicolas FRANCOIS
3,3001415
3,3001415
add a comment |Â
add a comment |Â
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