Infinite Integration using the ceiling function
up vote
5
down vote
favorite
$$int_0^infty frac{sin(xpi)}{lceil x rceil^2 + lceil x rceil} dx$$
My teacher recently gave me this and it's stumped me.
integration
|
show 2 more comments
up vote
5
down vote
favorite
$$int_0^infty frac{sin(xpi)}{lceil x rceil^2 + lceil x rceil} dx$$
My teacher recently gave me this and it's stumped me.
integration
Do we have to find a closed form, or just study the convergence? The latter is immediate
– Federico
Dec 4 at 20:14
He just said find the value of that.
– user546944
Dec 4 at 20:17
2
I would suggest to take things slowly. Starting with $lim_{nto infty} int_0^n frac{1}{lceil x^2 rceil + lceil x rceil} dx$ then split up the integral into n pieces so that we get rid of the ceil functions.
– Zacky
Dec 4 at 20:19
start dividing the integral in pieces where $frac1{lceil x^2rceil +lceil xrceil}$ is constant
– Masacroso
Dec 4 at 20:25
This is unpleasant, since it depends on the interleaving between the values of $n$ and $sqrt{m}$ for $n,minmathbb{N}$. Are you sure it is $lceil x^2rceil$ and not $lceil x rceil^2$?
– Jack D'Aurizio
Dec 4 at 20:43
|
show 2 more comments
up vote
5
down vote
favorite
up vote
5
down vote
favorite
$$int_0^infty frac{sin(xpi)}{lceil x rceil^2 + lceil x rceil} dx$$
My teacher recently gave me this and it's stumped me.
integration
$$int_0^infty frac{sin(xpi)}{lceil x rceil^2 + lceil x rceil} dx$$
My teacher recently gave me this and it's stumped me.
integration
integration
edited Dec 4 at 21:23
asked Dec 4 at 20:07
user546944
Do we have to find a closed form, or just study the convergence? The latter is immediate
– Federico
Dec 4 at 20:14
He just said find the value of that.
– user546944
Dec 4 at 20:17
2
I would suggest to take things slowly. Starting with $lim_{nto infty} int_0^n frac{1}{lceil x^2 rceil + lceil x rceil} dx$ then split up the integral into n pieces so that we get rid of the ceil functions.
– Zacky
Dec 4 at 20:19
start dividing the integral in pieces where $frac1{lceil x^2rceil +lceil xrceil}$ is constant
– Masacroso
Dec 4 at 20:25
This is unpleasant, since it depends on the interleaving between the values of $n$ and $sqrt{m}$ for $n,minmathbb{N}$. Are you sure it is $lceil x^2rceil$ and not $lceil x rceil^2$?
– Jack D'Aurizio
Dec 4 at 20:43
|
show 2 more comments
Do we have to find a closed form, or just study the convergence? The latter is immediate
– Federico
Dec 4 at 20:14
He just said find the value of that.
– user546944
Dec 4 at 20:17
2
I would suggest to take things slowly. Starting with $lim_{nto infty} int_0^n frac{1}{lceil x^2 rceil + lceil x rceil} dx$ then split up the integral into n pieces so that we get rid of the ceil functions.
– Zacky
Dec 4 at 20:19
start dividing the integral in pieces where $frac1{lceil x^2rceil +lceil xrceil}$ is constant
– Masacroso
Dec 4 at 20:25
This is unpleasant, since it depends on the interleaving between the values of $n$ and $sqrt{m}$ for $n,minmathbb{N}$. Are you sure it is $lceil x^2rceil$ and not $lceil x rceil^2$?
– Jack D'Aurizio
Dec 4 at 20:43
Do we have to find a closed form, or just study the convergence? The latter is immediate
– Federico
Dec 4 at 20:14
Do we have to find a closed form, or just study the convergence? The latter is immediate
– Federico
Dec 4 at 20:14
He just said find the value of that.
– user546944
Dec 4 at 20:17
He just said find the value of that.
– user546944
Dec 4 at 20:17
2
2
I would suggest to take things slowly. Starting with $lim_{nto infty} int_0^n frac{1}{lceil x^2 rceil + lceil x rceil} dx$ then split up the integral into n pieces so that we get rid of the ceil functions.
– Zacky
Dec 4 at 20:19
I would suggest to take things slowly. Starting with $lim_{nto infty} int_0^n frac{1}{lceil x^2 rceil + lceil x rceil} dx$ then split up the integral into n pieces so that we get rid of the ceil functions.
– Zacky
Dec 4 at 20:19
start dividing the integral in pieces where $frac1{lceil x^2rceil +lceil xrceil}$ is constant
– Masacroso
Dec 4 at 20:25
start dividing the integral in pieces where $frac1{lceil x^2rceil +lceil xrceil}$ is constant
– Masacroso
Dec 4 at 20:25
This is unpleasant, since it depends on the interleaving between the values of $n$ and $sqrt{m}$ for $n,minmathbb{N}$. Are you sure it is $lceil x^2rceil$ and not $lceil x rceil^2$?
– Jack D'Aurizio
Dec 4 at 20:43
This is unpleasant, since it depends on the interleaving between the values of $n$ and $sqrt{m}$ for $n,minmathbb{N}$. Are you sure it is $lceil x^2rceil$ and not $lceil x rceil^2$?
– Jack D'Aurizio
Dec 4 at 20:43
|
show 2 more comments
2 Answers
2
active
oldest
votes
up vote
8
down vote
$newcommand{bbx}[1]{,bbox[15px,border:1px groove navy]{displaystyle{#1}},}
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newcommand{bracks}[1]{leftlbrack,{#1},rightrbrack}
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newcommand{expo}[1]{,mathrm{e}^{#1},}
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newcommand{mrm}[1]{mathrm{#1}}
newcommand{pars}[1]{left(,{#1},right)}
newcommand{partiald}[3]{frac{partial^{#1} #2}{partial #3^{#1}}}
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begin{align}
&bbox[10px,#ffd]{int_{0}^{infty}{sinpars{pi x} over
leftlceil{x}rightrceil^{2} + leftlceil{x}rightrceil}
,dd x} =
sum_{k = 0}^{infty}int_{k}^{k + 1}
{sinpars{pi x} over
pars{k + 1}^{2} + pars{k + 1}},dd x
\[5mm] = &
{2 over pi}sum_{k = 0}^{infty}
{pars{-1}^{k} over pars{k + 1}pars{k + 2}} =
{2 over pi}bracks{%
sum_{k = 0}^{infty}{pars{-1}^{k} over k + 1} -
sum_{k = 0}^{infty}{pars{-1}^{k} over k + 2}}
\[5mm] = &
{2 over pi}bracks{%
-sum_{k = 1}^{infty}{pars{-1}^{k} over k} -
sum_{k = 2}^{infty}{pars{-1}^{k} over k}}
\[5mm] = &
-,{2 over pi}braces{%
sum_{k = 1}^{infty}{pars{-1}^{k} over k} +
bracks{1 + sum_{k = 1}^{infty}{pars{-1}^{k} over k}}} \[5mm] = &
-,{2 over pi}bracks{%
1 + 2sum_{k = 1}^{infty}{pars{-1}^{k} over k}} =
bbx{4lnpars{2} - 2 over pi} approx 0.2459
end{align}
add a comment |
up vote
3
down vote
Hint: break the integral up into
$$int_0^infty=int_0^1+int_1^2+int_2^3+cdots.$$
On each of these intervals the denominator takes a constant value, so you can bring it out of the integral sign and evaluate each. After that just sum all the terms you get.
1
Can the downvoter kindly explain?
– YiFan
Dec 5 at 2:07
add a comment |
Your 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
8
down vote
$newcommand{bbx}[1]{,bbox[15px,border:1px groove navy]{displaystyle{#1}},}
newcommand{braces}[1]{leftlbrace,{#1},rightrbrace}
newcommand{bracks}[1]{leftlbrack,{#1},rightrbrack}
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newcommand{totald}[3]{frac{mathrm{d}^{#1} #2}{mathrm{d} #3^{#1}}}
newcommand{verts}[1]{leftvert,{#1},rightvert}$
begin{align}
&bbox[10px,#ffd]{int_{0}^{infty}{sinpars{pi x} over
leftlceil{x}rightrceil^{2} + leftlceil{x}rightrceil}
,dd x} =
sum_{k = 0}^{infty}int_{k}^{k + 1}
{sinpars{pi x} over
pars{k + 1}^{2} + pars{k + 1}},dd x
\[5mm] = &
{2 over pi}sum_{k = 0}^{infty}
{pars{-1}^{k} over pars{k + 1}pars{k + 2}} =
{2 over pi}bracks{%
sum_{k = 0}^{infty}{pars{-1}^{k} over k + 1} -
sum_{k = 0}^{infty}{pars{-1}^{k} over k + 2}}
\[5mm] = &
{2 over pi}bracks{%
-sum_{k = 1}^{infty}{pars{-1}^{k} over k} -
sum_{k = 2}^{infty}{pars{-1}^{k} over k}}
\[5mm] = &
-,{2 over pi}braces{%
sum_{k = 1}^{infty}{pars{-1}^{k} over k} +
bracks{1 + sum_{k = 1}^{infty}{pars{-1}^{k} over k}}} \[5mm] = &
-,{2 over pi}bracks{%
1 + 2sum_{k = 1}^{infty}{pars{-1}^{k} over k}} =
bbx{4lnpars{2} - 2 over pi} approx 0.2459
end{align}
add a comment |
up vote
8
down vote
$newcommand{bbx}[1]{,bbox[15px,border:1px groove navy]{displaystyle{#1}},}
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newcommand{bracks}[1]{leftlbrack,{#1},rightrbrack}
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newcommand{root}[2]{,sqrt[#1]{,{#2},},}
newcommand{totald}[3]{frac{mathrm{d}^{#1} #2}{mathrm{d} #3^{#1}}}
newcommand{verts}[1]{leftvert,{#1},rightvert}$
begin{align}
&bbox[10px,#ffd]{int_{0}^{infty}{sinpars{pi x} over
leftlceil{x}rightrceil^{2} + leftlceil{x}rightrceil}
,dd x} =
sum_{k = 0}^{infty}int_{k}^{k + 1}
{sinpars{pi x} over
pars{k + 1}^{2} + pars{k + 1}},dd x
\[5mm] = &
{2 over pi}sum_{k = 0}^{infty}
{pars{-1}^{k} over pars{k + 1}pars{k + 2}} =
{2 over pi}bracks{%
sum_{k = 0}^{infty}{pars{-1}^{k} over k + 1} -
sum_{k = 0}^{infty}{pars{-1}^{k} over k + 2}}
\[5mm] = &
{2 over pi}bracks{%
-sum_{k = 1}^{infty}{pars{-1}^{k} over k} -
sum_{k = 2}^{infty}{pars{-1}^{k} over k}}
\[5mm] = &
-,{2 over pi}braces{%
sum_{k = 1}^{infty}{pars{-1}^{k} over k} +
bracks{1 + sum_{k = 1}^{infty}{pars{-1}^{k} over k}}} \[5mm] = &
-,{2 over pi}bracks{%
1 + 2sum_{k = 1}^{infty}{pars{-1}^{k} over k}} =
bbx{4lnpars{2} - 2 over pi} approx 0.2459
end{align}
add a comment |
up vote
8
down vote
up vote
8
down vote
$newcommand{bbx}[1]{,bbox[15px,border:1px groove navy]{displaystyle{#1}},}
newcommand{braces}[1]{leftlbrace,{#1},rightrbrace}
newcommand{bracks}[1]{leftlbrack,{#1},rightrbrack}
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newcommand{ds}[1]{displaystyle{#1}}
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newcommand{mrm}[1]{mathrm{#1}}
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newcommand{root}[2]{,sqrt[#1]{,{#2},},}
newcommand{totald}[3]{frac{mathrm{d}^{#1} #2}{mathrm{d} #3^{#1}}}
newcommand{verts}[1]{leftvert,{#1},rightvert}$
begin{align}
&bbox[10px,#ffd]{int_{0}^{infty}{sinpars{pi x} over
leftlceil{x}rightrceil^{2} + leftlceil{x}rightrceil}
,dd x} =
sum_{k = 0}^{infty}int_{k}^{k + 1}
{sinpars{pi x} over
pars{k + 1}^{2} + pars{k + 1}},dd x
\[5mm] = &
{2 over pi}sum_{k = 0}^{infty}
{pars{-1}^{k} over pars{k + 1}pars{k + 2}} =
{2 over pi}bracks{%
sum_{k = 0}^{infty}{pars{-1}^{k} over k + 1} -
sum_{k = 0}^{infty}{pars{-1}^{k} over k + 2}}
\[5mm] = &
{2 over pi}bracks{%
-sum_{k = 1}^{infty}{pars{-1}^{k} over k} -
sum_{k = 2}^{infty}{pars{-1}^{k} over k}}
\[5mm] = &
-,{2 over pi}braces{%
sum_{k = 1}^{infty}{pars{-1}^{k} over k} +
bracks{1 + sum_{k = 1}^{infty}{pars{-1}^{k} over k}}} \[5mm] = &
-,{2 over pi}bracks{%
1 + 2sum_{k = 1}^{infty}{pars{-1}^{k} over k}} =
bbx{4lnpars{2} - 2 over pi} approx 0.2459
end{align}
$newcommand{bbx}[1]{,bbox[15px,border:1px groove navy]{displaystyle{#1}},}
newcommand{braces}[1]{leftlbrace,{#1},rightrbrace}
newcommand{bracks}[1]{leftlbrack,{#1},rightrbrack}
newcommand{dd}{mathrm{d}}
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newcommand{verts}[1]{leftvert,{#1},rightvert}$
begin{align}
&bbox[10px,#ffd]{int_{0}^{infty}{sinpars{pi x} over
leftlceil{x}rightrceil^{2} + leftlceil{x}rightrceil}
,dd x} =
sum_{k = 0}^{infty}int_{k}^{k + 1}
{sinpars{pi x} over
pars{k + 1}^{2} + pars{k + 1}},dd x
\[5mm] = &
{2 over pi}sum_{k = 0}^{infty}
{pars{-1}^{k} over pars{k + 1}pars{k + 2}} =
{2 over pi}bracks{%
sum_{k = 0}^{infty}{pars{-1}^{k} over k + 1} -
sum_{k = 0}^{infty}{pars{-1}^{k} over k + 2}}
\[5mm] = &
{2 over pi}bracks{%
-sum_{k = 1}^{infty}{pars{-1}^{k} over k} -
sum_{k = 2}^{infty}{pars{-1}^{k} over k}}
\[5mm] = &
-,{2 over pi}braces{%
sum_{k = 1}^{infty}{pars{-1}^{k} over k} +
bracks{1 + sum_{k = 1}^{infty}{pars{-1}^{k} over k}}} \[5mm] = &
-,{2 over pi}bracks{%
1 + 2sum_{k = 1}^{infty}{pars{-1}^{k} over k}} =
bbx{4lnpars{2} - 2 over pi} approx 0.2459
end{align}
edited Dec 5 at 2:49
answered Dec 5 at 2:41
Felix Marin
66.8k7107139
66.8k7107139
add a comment |
add a comment |
up vote
3
down vote
Hint: break the integral up into
$$int_0^infty=int_0^1+int_1^2+int_2^3+cdots.$$
On each of these intervals the denominator takes a constant value, so you can bring it out of the integral sign and evaluate each. After that just sum all the terms you get.
1
Can the downvoter kindly explain?
– YiFan
Dec 5 at 2:07
add a comment |
up vote
3
down vote
Hint: break the integral up into
$$int_0^infty=int_0^1+int_1^2+int_2^3+cdots.$$
On each of these intervals the denominator takes a constant value, so you can bring it out of the integral sign and evaluate each. After that just sum all the terms you get.
1
Can the downvoter kindly explain?
– YiFan
Dec 5 at 2:07
add a comment |
up vote
3
down vote
up vote
3
down vote
Hint: break the integral up into
$$int_0^infty=int_0^1+int_1^2+int_2^3+cdots.$$
On each of these intervals the denominator takes a constant value, so you can bring it out of the integral sign and evaluate each. After that just sum all the terms you get.
Hint: break the integral up into
$$int_0^infty=int_0^1+int_1^2+int_2^3+cdots.$$
On each of these intervals the denominator takes a constant value, so you can bring it out of the integral sign and evaluate each. After that just sum all the terms you get.
answered Dec 4 at 22:58
YiFan
2,1761421
2,1761421
1
Can the downvoter kindly explain?
– YiFan
Dec 5 at 2:07
add a comment |
1
Can the downvoter kindly explain?
– YiFan
Dec 5 at 2:07
1
1
Can the downvoter kindly explain?
– YiFan
Dec 5 at 2:07
Can the downvoter kindly explain?
– YiFan
Dec 5 at 2:07
add a comment |
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Do we have to find a closed form, or just study the convergence? The latter is immediate
– Federico
Dec 4 at 20:14
He just said find the value of that.
– user546944
Dec 4 at 20:17
2
I would suggest to take things slowly. Starting with $lim_{nto infty} int_0^n frac{1}{lceil x^2 rceil + lceil x rceil} dx$ then split up the integral into n pieces so that we get rid of the ceil functions.
– Zacky
Dec 4 at 20:19
start dividing the integral in pieces where $frac1{lceil x^2rceil +lceil xrceil}$ is constant
– Masacroso
Dec 4 at 20:25
This is unpleasant, since it depends on the interleaving between the values of $n$ and $sqrt{m}$ for $n,minmathbb{N}$. Are you sure it is $lceil x^2rceil$ and not $lceil x rceil^2$?
– Jack D'Aurizio
Dec 4 at 20:43