How does this infinite series simplify to an integral? The 2019 Stack Overflow Developer Survey Results Are In Announcing the arrival of Valued Associate #679: Cesar Manara Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)Infinite Series ManipulationsHow do I solve this integral? (looking for hints)Finding Sum for Infinite SeriesSimplify Infinite Series Involving Gamma Function $Gamma$How to simplify this integral?Does this infinite series converge or diverge?Sum of this infinite series…Why does Improper Integral Diverge?Infinite series containing positive and negative termsInfinite series sum which have infinite terms
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How does this infinite series simplify to an integral?
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How does this infinite series simplify to an integral?
The 2019 Stack Overflow Developer Survey Results Are In
Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)Infinite Series ManipulationsHow do I solve this integral? (looking for hints)Finding Sum for Infinite SeriesSimplify Infinite Series Involving Gamma Function $Gamma$How to simplify this integral?Does this infinite series converge or diverge?Sum of this infinite series…Why does Improper Integral Diverge?Infinite series containing positive and negative termsInfinite series sum which have infinite terms
$begingroup$
How does the infinite series in the link above simplify to that integral?
$$1-frac14+frac17-frac110+cdots=int_0^1fracdx1+x^3$$
I thought of simplifying the series to the sum to infinity of $frac16n-5 - frac16n-2$, but this did not help.
integration sequences-and-series power-series improper-integrals
$endgroup$
add a comment |
$begingroup$
How does the infinite series in the link above simplify to that integral?
$$1-frac14+frac17-frac110+cdots=int_0^1fracdx1+x^3$$
I thought of simplifying the series to the sum to infinity of $frac16n-5 - frac16n-2$, but this did not help.
integration sequences-and-series power-series improper-integrals
$endgroup$
1
$begingroup$
en.wikipedia.org/wiki/Binomial_series $$(1+x^3)^-1$$
$endgroup$
– lab bhattacharjee
4 hours ago
$begingroup$
It can be obtained by integrating term by term the infinite series expansion of $(1+x^3)^-1$.
$endgroup$
– StubbornAtom
4 hours ago
add a comment |
$begingroup$
How does the infinite series in the link above simplify to that integral?
$$1-frac14+frac17-frac110+cdots=int_0^1fracdx1+x^3$$
I thought of simplifying the series to the sum to infinity of $frac16n-5 - frac16n-2$, but this did not help.
integration sequences-and-series power-series improper-integrals
$endgroup$
How does the infinite series in the link above simplify to that integral?
$$1-frac14+frac17-frac110+cdots=int_0^1fracdx1+x^3$$
I thought of simplifying the series to the sum to infinity of $frac16n-5 - frac16n-2$, but this did not help.
integration sequences-and-series power-series improper-integrals
integration sequences-and-series power-series improper-integrals
edited 4 hours ago
Zacky
7,87511062
7,87511062
asked 4 hours ago
ShreeShree
114
114
1
$begingroup$
en.wikipedia.org/wiki/Binomial_series $$(1+x^3)^-1$$
$endgroup$
– lab bhattacharjee
4 hours ago
$begingroup$
It can be obtained by integrating term by term the infinite series expansion of $(1+x^3)^-1$.
$endgroup$
– StubbornAtom
4 hours ago
add a comment |
1
$begingroup$
en.wikipedia.org/wiki/Binomial_series $$(1+x^3)^-1$$
$endgroup$
– lab bhattacharjee
4 hours ago
$begingroup$
It can be obtained by integrating term by term the infinite series expansion of $(1+x^3)^-1$.
$endgroup$
– StubbornAtom
4 hours ago
1
1
$begingroup$
en.wikipedia.org/wiki/Binomial_series $$(1+x^3)^-1$$
$endgroup$
– lab bhattacharjee
4 hours ago
$begingroup$
en.wikipedia.org/wiki/Binomial_series $$(1+x^3)^-1$$
$endgroup$
– lab bhattacharjee
4 hours ago
$begingroup$
It can be obtained by integrating term by term the infinite series expansion of $(1+x^3)^-1$.
$endgroup$
– StubbornAtom
4 hours ago
$begingroup$
It can be obtained by integrating term by term the infinite series expansion of $(1+x^3)^-1$.
$endgroup$
– StubbornAtom
4 hours ago
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
$$int_0^1fracdx1-(-x)^3=int_0^1sum_n=0^infty(-x)^3ndx=sum_n=0^infty(-1)^3nint_0^1x^3ndx$$
$$=sum_n=0^inftyfrac(-1)^3n3n+1= 1-frac14+frac17-frac110+cdots $$
$endgroup$
$begingroup$
For those who aren't clear on the first equality, it's a geometric series formula.
$endgroup$
– Alexis Olson
1 hour ago
add a comment |
$begingroup$
for $x$ real, $ngeq 0$ integer
beginalignfrac11+x^3&=frac1-(-x^3)^n+11-(-x^3)+frac(-x^3)^n+11-(-x^3)\
&=frac1-(-x^3)^n+11-(-x^3)+frac(-x^3)^n+11+x^3\
endalign
For $xneq 1$, $ngeq 0$ integer, beginalignsum_k=0^n x^k=frac1-x^n+11-xendalign
Therefore,
beginalignint_0^1 frac11+x^3,dx&=int_0^1 left(sum_k=0^n (-x^3)^kright),dx+int_0^1 frac(-x^3)^n+11+x^3,dx\
&=sum_k=0^n left(int_0^1 (-x^3)^k,dxright)+int_0^1 frac(-x^3)^n+11+x^3,dx\
&=sum_k=0^n frac(-1)^k3k+1+int_0^1 frac(-x^3)^n+11+x^3,dx\
endalign
For $xin[0;1],ngeq 0$, integer,
beginalignfracx^3(n+1)1+x^3leq x^3(n+1)endalign
and,
beginalignint_0^1 x^3(n+1),dx=frac13n+4endalign
Therefore,
beginalignleft|int_0^1 frac(-x^3)^n+11+x^3,dxright|leq frac13n+4endalign
beginalignleft|int_0^1 frac11+x^3,dx-sum_k=0^n frac(-1)^k3k+1right|leq frac13n+4endalign
Therefore,
beginalignboxedint_0^1 frac11+x^3,dx=sum_k=0^infty frac(-1)^k3k+1endalign
$endgroup$
add a comment |
$begingroup$
If $lvert xrvert<1$, let$$f(x)=sum_n=0^inftyfracx^3n+13n+1.$$Then $$f'(x)=sum_n=0^infty x^3n=frac11-x^3.$$Thereforebeginalign1-frac14+frac17-frac110+cdots&=lim_xto1f(x)\&=int_0^1f'(x),mathrm dx\&=int_0^1frac11-x^3,mathrm dx.endalign
$endgroup$
add a comment |
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3 Answers
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active
oldest
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3 Answers
3
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oldest
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votes
$begingroup$
$$int_0^1fracdx1-(-x)^3=int_0^1sum_n=0^infty(-x)^3ndx=sum_n=0^infty(-1)^3nint_0^1x^3ndx$$
$$=sum_n=0^inftyfrac(-1)^3n3n+1= 1-frac14+frac17-frac110+cdots $$
$endgroup$
$begingroup$
For those who aren't clear on the first equality, it's a geometric series formula.
$endgroup$
– Alexis Olson
1 hour ago
add a comment |
$begingroup$
$$int_0^1fracdx1-(-x)^3=int_0^1sum_n=0^infty(-x)^3ndx=sum_n=0^infty(-1)^3nint_0^1x^3ndx$$
$$=sum_n=0^inftyfrac(-1)^3n3n+1= 1-frac14+frac17-frac110+cdots $$
$endgroup$
$begingroup$
For those who aren't clear on the first equality, it's a geometric series formula.
$endgroup$
– Alexis Olson
1 hour ago
add a comment |
$begingroup$
$$int_0^1fracdx1-(-x)^3=int_0^1sum_n=0^infty(-x)^3ndx=sum_n=0^infty(-1)^3nint_0^1x^3ndx$$
$$=sum_n=0^inftyfrac(-1)^3n3n+1= 1-frac14+frac17-frac110+cdots $$
$endgroup$
$$int_0^1fracdx1-(-x)^3=int_0^1sum_n=0^infty(-x)^3ndx=sum_n=0^infty(-1)^3nint_0^1x^3ndx$$
$$=sum_n=0^inftyfrac(-1)^3n3n+1= 1-frac14+frac17-frac110+cdots $$
edited 18 mins ago
answered 4 hours ago
HAMIDINE SOUMAREHAMIDINE SOUMARE
2,194212
2,194212
$begingroup$
For those who aren't clear on the first equality, it's a geometric series formula.
$endgroup$
– Alexis Olson
1 hour ago
add a comment |
$begingroup$
For those who aren't clear on the first equality, it's a geometric series formula.
$endgroup$
– Alexis Olson
1 hour ago
$begingroup$
For those who aren't clear on the first equality, it's a geometric series formula.
$endgroup$
– Alexis Olson
1 hour ago
$begingroup$
For those who aren't clear on the first equality, it's a geometric series formula.
$endgroup$
– Alexis Olson
1 hour ago
add a comment |
$begingroup$
for $x$ real, $ngeq 0$ integer
beginalignfrac11+x^3&=frac1-(-x^3)^n+11-(-x^3)+frac(-x^3)^n+11-(-x^3)\
&=frac1-(-x^3)^n+11-(-x^3)+frac(-x^3)^n+11+x^3\
endalign
For $xneq 1$, $ngeq 0$ integer, beginalignsum_k=0^n x^k=frac1-x^n+11-xendalign
Therefore,
beginalignint_0^1 frac11+x^3,dx&=int_0^1 left(sum_k=0^n (-x^3)^kright),dx+int_0^1 frac(-x^3)^n+11+x^3,dx\
&=sum_k=0^n left(int_0^1 (-x^3)^k,dxright)+int_0^1 frac(-x^3)^n+11+x^3,dx\
&=sum_k=0^n frac(-1)^k3k+1+int_0^1 frac(-x^3)^n+11+x^3,dx\
endalign
For $xin[0;1],ngeq 0$, integer,
beginalignfracx^3(n+1)1+x^3leq x^3(n+1)endalign
and,
beginalignint_0^1 x^3(n+1),dx=frac13n+4endalign
Therefore,
beginalignleft|int_0^1 frac(-x^3)^n+11+x^3,dxright|leq frac13n+4endalign
beginalignleft|int_0^1 frac11+x^3,dx-sum_k=0^n frac(-1)^k3k+1right|leq frac13n+4endalign
Therefore,
beginalignboxedint_0^1 frac11+x^3,dx=sum_k=0^infty frac(-1)^k3k+1endalign
$endgroup$
add a comment |
$begingroup$
for $x$ real, $ngeq 0$ integer
beginalignfrac11+x^3&=frac1-(-x^3)^n+11-(-x^3)+frac(-x^3)^n+11-(-x^3)\
&=frac1-(-x^3)^n+11-(-x^3)+frac(-x^3)^n+11+x^3\
endalign
For $xneq 1$, $ngeq 0$ integer, beginalignsum_k=0^n x^k=frac1-x^n+11-xendalign
Therefore,
beginalignint_0^1 frac11+x^3,dx&=int_0^1 left(sum_k=0^n (-x^3)^kright),dx+int_0^1 frac(-x^3)^n+11+x^3,dx\
&=sum_k=0^n left(int_0^1 (-x^3)^k,dxright)+int_0^1 frac(-x^3)^n+11+x^3,dx\
&=sum_k=0^n frac(-1)^k3k+1+int_0^1 frac(-x^3)^n+11+x^3,dx\
endalign
For $xin[0;1],ngeq 0$, integer,
beginalignfracx^3(n+1)1+x^3leq x^3(n+1)endalign
and,
beginalignint_0^1 x^3(n+1),dx=frac13n+4endalign
Therefore,
beginalignleft|int_0^1 frac(-x^3)^n+11+x^3,dxright|leq frac13n+4endalign
beginalignleft|int_0^1 frac11+x^3,dx-sum_k=0^n frac(-1)^k3k+1right|leq frac13n+4endalign
Therefore,
beginalignboxedint_0^1 frac11+x^3,dx=sum_k=0^infty frac(-1)^k3k+1endalign
$endgroup$
add a comment |
$begingroup$
for $x$ real, $ngeq 0$ integer
beginalignfrac11+x^3&=frac1-(-x^3)^n+11-(-x^3)+frac(-x^3)^n+11-(-x^3)\
&=frac1-(-x^3)^n+11-(-x^3)+frac(-x^3)^n+11+x^3\
endalign
For $xneq 1$, $ngeq 0$ integer, beginalignsum_k=0^n x^k=frac1-x^n+11-xendalign
Therefore,
beginalignint_0^1 frac11+x^3,dx&=int_0^1 left(sum_k=0^n (-x^3)^kright),dx+int_0^1 frac(-x^3)^n+11+x^3,dx\
&=sum_k=0^n left(int_0^1 (-x^3)^k,dxright)+int_0^1 frac(-x^3)^n+11+x^3,dx\
&=sum_k=0^n frac(-1)^k3k+1+int_0^1 frac(-x^3)^n+11+x^3,dx\
endalign
For $xin[0;1],ngeq 0$, integer,
beginalignfracx^3(n+1)1+x^3leq x^3(n+1)endalign
and,
beginalignint_0^1 x^3(n+1),dx=frac13n+4endalign
Therefore,
beginalignleft|int_0^1 frac(-x^3)^n+11+x^3,dxright|leq frac13n+4endalign
beginalignleft|int_0^1 frac11+x^3,dx-sum_k=0^n frac(-1)^k3k+1right|leq frac13n+4endalign
Therefore,
beginalignboxedint_0^1 frac11+x^3,dx=sum_k=0^infty frac(-1)^k3k+1endalign
$endgroup$
for $x$ real, $ngeq 0$ integer
beginalignfrac11+x^3&=frac1-(-x^3)^n+11-(-x^3)+frac(-x^3)^n+11-(-x^3)\
&=frac1-(-x^3)^n+11-(-x^3)+frac(-x^3)^n+11+x^3\
endalign
For $xneq 1$, $ngeq 0$ integer, beginalignsum_k=0^n x^k=frac1-x^n+11-xendalign
Therefore,
beginalignint_0^1 frac11+x^3,dx&=int_0^1 left(sum_k=0^n (-x^3)^kright),dx+int_0^1 frac(-x^3)^n+11+x^3,dx\
&=sum_k=0^n left(int_0^1 (-x^3)^k,dxright)+int_0^1 frac(-x^3)^n+11+x^3,dx\
&=sum_k=0^n frac(-1)^k3k+1+int_0^1 frac(-x^3)^n+11+x^3,dx\
endalign
For $xin[0;1],ngeq 0$, integer,
beginalignfracx^3(n+1)1+x^3leq x^3(n+1)endalign
and,
beginalignint_0^1 x^3(n+1),dx=frac13n+4endalign
Therefore,
beginalignleft|int_0^1 frac(-x^3)^n+11+x^3,dxright|leq frac13n+4endalign
beginalignleft|int_0^1 frac11+x^3,dx-sum_k=0^n frac(-1)^k3k+1right|leq frac13n+4endalign
Therefore,
beginalignboxedint_0^1 frac11+x^3,dx=sum_k=0^infty frac(-1)^k3k+1endalign
answered 3 hours ago
FDPFDP
6,12211929
6,12211929
add a comment |
add a comment |
$begingroup$
If $lvert xrvert<1$, let$$f(x)=sum_n=0^inftyfracx^3n+13n+1.$$Then $$f'(x)=sum_n=0^infty x^3n=frac11-x^3.$$Thereforebeginalign1-frac14+frac17-frac110+cdots&=lim_xto1f(x)\&=int_0^1f'(x),mathrm dx\&=int_0^1frac11-x^3,mathrm dx.endalign
$endgroup$
add a comment |
$begingroup$
If $lvert xrvert<1$, let$$f(x)=sum_n=0^inftyfracx^3n+13n+1.$$Then $$f'(x)=sum_n=0^infty x^3n=frac11-x^3.$$Thereforebeginalign1-frac14+frac17-frac110+cdots&=lim_xto1f(x)\&=int_0^1f'(x),mathrm dx\&=int_0^1frac11-x^3,mathrm dx.endalign
$endgroup$
add a comment |
$begingroup$
If $lvert xrvert<1$, let$$f(x)=sum_n=0^inftyfracx^3n+13n+1.$$Then $$f'(x)=sum_n=0^infty x^3n=frac11-x^3.$$Thereforebeginalign1-frac14+frac17-frac110+cdots&=lim_xto1f(x)\&=int_0^1f'(x),mathrm dx\&=int_0^1frac11-x^3,mathrm dx.endalign
$endgroup$
If $lvert xrvert<1$, let$$f(x)=sum_n=0^inftyfracx^3n+13n+1.$$Then $$f'(x)=sum_n=0^infty x^3n=frac11-x^3.$$Thereforebeginalign1-frac14+frac17-frac110+cdots&=lim_xto1f(x)\&=int_0^1f'(x),mathrm dx\&=int_0^1frac11-x^3,mathrm dx.endalign
answered 4 hours ago
José Carlos SantosJosé Carlos Santos
174k23133243
174k23133243
add a comment |
add a comment |
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1
$begingroup$
en.wikipedia.org/wiki/Binomial_series $$(1+x^3)^-1$$
$endgroup$
– lab bhattacharjee
4 hours ago
$begingroup$
It can be obtained by integrating term by term the infinite series expansion of $(1+x^3)^-1$.
$endgroup$
– StubbornAtom
4 hours ago