How to prove that $intlimits_0^{pi} e^{sin^2(x)}dx > {3over2}pi$? [closed]











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How to prove that $intlimits_0^{pi} e^{sin^2(x)} dx > {3 over 2}pi$?










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closed as off-topic by Rebellos, Jyrki Lahtonen, amWhy, José Carlos Santos, DRF Dec 4 at 22:49


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Rebellos, Jyrki Lahtonen, amWhy, José Carlos Santos, DRF

If this question can be reworded to fit the rules in the help center, please edit the question.













  • Could you please edit the question, the math notations are not showing.
    – John_Wick
    Nov 29 at 21:53






  • 1




    I don't understand why anyone would down-vote this question. It's perfect fine and compiles with the requirements of the page.
    – DavidG
    Nov 30 at 3:48






  • 5




    @DavidG Hover your cursor over the voting arrows... "This question (shows / does not show any) research effort".
    – epimorphic
    Dec 4 at 17:52






  • 1




    @DavidG Go to How to ask a good question and report back to us in which ways this question satisfies any of the criteria. This is a problem statement question, essentially expecting answerers to do this users work for them. Hence the downvote, hence the close votes. This site is not a "do my work/proof for me" service.
    – amWhy
    Dec 4 at 22:42










  • @amWhy - will do. Thanks for the link.
    – DavidG
    Dec 4 at 22:44















up vote
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How to prove that $intlimits_0^{pi} e^{sin^2(x)} dx > {3 over 2}pi$?










share|cite|improve this question















closed as off-topic by Rebellos, Jyrki Lahtonen, amWhy, José Carlos Santos, DRF Dec 4 at 22:49


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Rebellos, Jyrki Lahtonen, amWhy, José Carlos Santos, DRF

If this question can be reworded to fit the rules in the help center, please edit the question.













  • Could you please edit the question, the math notations are not showing.
    – John_Wick
    Nov 29 at 21:53






  • 1




    I don't understand why anyone would down-vote this question. It's perfect fine and compiles with the requirements of the page.
    – DavidG
    Nov 30 at 3:48






  • 5




    @DavidG Hover your cursor over the voting arrows... "This question (shows / does not show any) research effort".
    – epimorphic
    Dec 4 at 17:52






  • 1




    @DavidG Go to How to ask a good question and report back to us in which ways this question satisfies any of the criteria. This is a problem statement question, essentially expecting answerers to do this users work for them. Hence the downvote, hence the close votes. This site is not a "do my work/proof for me" service.
    – amWhy
    Dec 4 at 22:42










  • @amWhy - will do. Thanks for the link.
    – DavidG
    Dec 4 at 22:44













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How to prove that $intlimits_0^{pi} e^{sin^2(x)} dx > {3 over 2}pi$?










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How to prove that $intlimits_0^{pi} e^{sin^2(x)} dx > {3 over 2}pi$?







definite-integrals integral-inequality






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edited Nov 29 at 21:56









Bernard

117k637109




117k637109










asked Nov 29 at 21:52









TBox

233




233




closed as off-topic by Rebellos, Jyrki Lahtonen, amWhy, José Carlos Santos, DRF Dec 4 at 22:49


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Rebellos, Jyrki Lahtonen, amWhy, José Carlos Santos, DRF

If this question can be reworded to fit the rules in the help center, please edit the question.




closed as off-topic by Rebellos, Jyrki Lahtonen, amWhy, José Carlos Santos, DRF Dec 4 at 22:49


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Rebellos, Jyrki Lahtonen, amWhy, José Carlos Santos, DRF

If this question can be reworded to fit the rules in the help center, please edit the question.












  • Could you please edit the question, the math notations are not showing.
    – John_Wick
    Nov 29 at 21:53






  • 1




    I don't understand why anyone would down-vote this question. It's perfect fine and compiles with the requirements of the page.
    – DavidG
    Nov 30 at 3:48






  • 5




    @DavidG Hover your cursor over the voting arrows... "This question (shows / does not show any) research effort".
    – epimorphic
    Dec 4 at 17:52






  • 1




    @DavidG Go to How to ask a good question and report back to us in which ways this question satisfies any of the criteria. This is a problem statement question, essentially expecting answerers to do this users work for them. Hence the downvote, hence the close votes. This site is not a "do my work/proof for me" service.
    – amWhy
    Dec 4 at 22:42










  • @amWhy - will do. Thanks for the link.
    – DavidG
    Dec 4 at 22:44


















  • Could you please edit the question, the math notations are not showing.
    – John_Wick
    Nov 29 at 21:53






  • 1




    I don't understand why anyone would down-vote this question. It's perfect fine and compiles with the requirements of the page.
    – DavidG
    Nov 30 at 3:48






  • 5




    @DavidG Hover your cursor over the voting arrows... "This question (shows / does not show any) research effort".
    – epimorphic
    Dec 4 at 17:52






  • 1




    @DavidG Go to How to ask a good question and report back to us in which ways this question satisfies any of the criteria. This is a problem statement question, essentially expecting answerers to do this users work for them. Hence the downvote, hence the close votes. This site is not a "do my work/proof for me" service.
    – amWhy
    Dec 4 at 22:42










  • @amWhy - will do. Thanks for the link.
    – DavidG
    Dec 4 at 22:44
















Could you please edit the question, the math notations are not showing.
– John_Wick
Nov 29 at 21:53




Could you please edit the question, the math notations are not showing.
– John_Wick
Nov 29 at 21:53




1




1




I don't understand why anyone would down-vote this question. It's perfect fine and compiles with the requirements of the page.
– DavidG
Nov 30 at 3:48




I don't understand why anyone would down-vote this question. It's perfect fine and compiles with the requirements of the page.
– DavidG
Nov 30 at 3:48




5




5




@DavidG Hover your cursor over the voting arrows... "This question (shows / does not show any) research effort".
– epimorphic
Dec 4 at 17:52




@DavidG Hover your cursor over the voting arrows... "This question (shows / does not show any) research effort".
– epimorphic
Dec 4 at 17:52




1




1




@DavidG Go to How to ask a good question and report back to us in which ways this question satisfies any of the criteria. This is a problem statement question, essentially expecting answerers to do this users work for them. Hence the downvote, hence the close votes. This site is not a "do my work/proof for me" service.
– amWhy
Dec 4 at 22:42




@DavidG Go to How to ask a good question and report back to us in which ways this question satisfies any of the criteria. This is a problem statement question, essentially expecting answerers to do this users work for them. Hence the downvote, hence the close votes. This site is not a "do my work/proof for me" service.
– amWhy
Dec 4 at 22:42












@amWhy - will do. Thanks for the link.
– DavidG
Dec 4 at 22:44




@amWhy - will do. Thanks for the link.
– DavidG
Dec 4 at 22:44










3 Answers
3






active

oldest

votes

















up vote
8
down vote













Use the inequality $e^tge 1+t$, valid for all $t$, to get:
$$
int_0^pi e^{sin^2x}dxgeint_0^pi(1+sin^2x)dx=int_0^pileft(frac32 + frac12cos 2xright),dx
$$

You should be able to take it from here. The inequality is in fact strict, because the difference $e^{sin^2x}-(1+sin^2x)$ is continuous, non-negative and not identically zero.






share|cite|improve this answer























  • I've taken and it equals to $int_0^pi(1+sin^2x)dx = {3over2}pi$ But is it really right to use $e^tge 1+t$?
    – TBox
    Nov 29 at 22:20












  • $$e^t > 1+t$$ is true for all nonzero real numbers, hence it is not necessary to use the second term of Taylor expansion.
    – Crostul
    Nov 29 at 22:22












  • got it, thank you!
    – TBox
    Nov 29 at 22:28










  • @ArseniyBakaev The inequality $e^tge 1+t$ is easily proven: See math.stackexchange.com/q/1330815/215011
    – grand_chat
    Nov 29 at 22:28












  • @Crostul Right, and the justification that $int_0^pi sin^4 (x) dx>0$ will equally apply to $int_0^pi e^{sin^2x}dx > int_0^pi (1+sin^2x)dx$.
    – grand_chat
    Nov 29 at 22:55




















up vote
0
down vote













We can also use Taylor expansion: $e^{sin^2(x)}=1+sin^2(x)+sin^4(x)/2+...$ and integrate it from $0$ to $pi$



$int_0^pi(1+sin^2(x)+(sin^4(x))/2)dx=(27pi)/16 ≈ 5.3014 > 3pi/2$






share|cite|improve this answer























  • Why post this, which copies the idea of a previous answer, only more clumsily?
    – Did
    Dec 5 at 0:06


















up vote
-2
down vote













The integral is a Bessel function:



$$sqrt{e} pi I_0left(frac{1}{2}right)$$



which has numerical value $5.50843$, which is indeed less than $3 pi/2$. This, it would seem, answers the question completely in a principled, and correct manner. One might try any number of other techniques, but I cannot see how any could be better than solving the integral exactly.






share|cite|improve this answer























  • Is it possible to compare without Bessel function?
    – TBox
    Nov 29 at 21:57










  • The only other way to compare would be a numerical integration.
    – David G. Stork
    Nov 29 at 21:58










  • @DavidG.Stork Bessel function does the trick, but in order to just find a soft result, you can go by the ML inequality as elaborated below.
    – Rebellos
    Nov 29 at 22:03










  • "The only other way to compare would be a numerical integration" Not true.
    – Did
    Dec 5 at 0:05


















3 Answers
3






active

oldest

votes








3 Answers
3






active

oldest

votes









active

oldest

votes






active

oldest

votes








up vote
8
down vote













Use the inequality $e^tge 1+t$, valid for all $t$, to get:
$$
int_0^pi e^{sin^2x}dxgeint_0^pi(1+sin^2x)dx=int_0^pileft(frac32 + frac12cos 2xright),dx
$$

You should be able to take it from here. The inequality is in fact strict, because the difference $e^{sin^2x}-(1+sin^2x)$ is continuous, non-negative and not identically zero.






share|cite|improve this answer























  • I've taken and it equals to $int_0^pi(1+sin^2x)dx = {3over2}pi$ But is it really right to use $e^tge 1+t$?
    – TBox
    Nov 29 at 22:20












  • $$e^t > 1+t$$ is true for all nonzero real numbers, hence it is not necessary to use the second term of Taylor expansion.
    – Crostul
    Nov 29 at 22:22












  • got it, thank you!
    – TBox
    Nov 29 at 22:28










  • @ArseniyBakaev The inequality $e^tge 1+t$ is easily proven: See math.stackexchange.com/q/1330815/215011
    – grand_chat
    Nov 29 at 22:28












  • @Crostul Right, and the justification that $int_0^pi sin^4 (x) dx>0$ will equally apply to $int_0^pi e^{sin^2x}dx > int_0^pi (1+sin^2x)dx$.
    – grand_chat
    Nov 29 at 22:55

















up vote
8
down vote













Use the inequality $e^tge 1+t$, valid for all $t$, to get:
$$
int_0^pi e^{sin^2x}dxgeint_0^pi(1+sin^2x)dx=int_0^pileft(frac32 + frac12cos 2xright),dx
$$

You should be able to take it from here. The inequality is in fact strict, because the difference $e^{sin^2x}-(1+sin^2x)$ is continuous, non-negative and not identically zero.






share|cite|improve this answer























  • I've taken and it equals to $int_0^pi(1+sin^2x)dx = {3over2}pi$ But is it really right to use $e^tge 1+t$?
    – TBox
    Nov 29 at 22:20












  • $$e^t > 1+t$$ is true for all nonzero real numbers, hence it is not necessary to use the second term of Taylor expansion.
    – Crostul
    Nov 29 at 22:22












  • got it, thank you!
    – TBox
    Nov 29 at 22:28










  • @ArseniyBakaev The inequality $e^tge 1+t$ is easily proven: See math.stackexchange.com/q/1330815/215011
    – grand_chat
    Nov 29 at 22:28












  • @Crostul Right, and the justification that $int_0^pi sin^4 (x) dx>0$ will equally apply to $int_0^pi e^{sin^2x}dx > int_0^pi (1+sin^2x)dx$.
    – grand_chat
    Nov 29 at 22:55















up vote
8
down vote










up vote
8
down vote









Use the inequality $e^tge 1+t$, valid for all $t$, to get:
$$
int_0^pi e^{sin^2x}dxgeint_0^pi(1+sin^2x)dx=int_0^pileft(frac32 + frac12cos 2xright),dx
$$

You should be able to take it from here. The inequality is in fact strict, because the difference $e^{sin^2x}-(1+sin^2x)$ is continuous, non-negative and not identically zero.






share|cite|improve this answer














Use the inequality $e^tge 1+t$, valid for all $t$, to get:
$$
int_0^pi e^{sin^2x}dxgeint_0^pi(1+sin^2x)dx=int_0^pileft(frac32 + frac12cos 2xright),dx
$$

You should be able to take it from here. The inequality is in fact strict, because the difference $e^{sin^2x}-(1+sin^2x)$ is continuous, non-negative and not identically zero.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Nov 29 at 23:42

























answered Nov 29 at 22:10









grand_chat

19.8k11225




19.8k11225












  • I've taken and it equals to $int_0^pi(1+sin^2x)dx = {3over2}pi$ But is it really right to use $e^tge 1+t$?
    – TBox
    Nov 29 at 22:20












  • $$e^t > 1+t$$ is true for all nonzero real numbers, hence it is not necessary to use the second term of Taylor expansion.
    – Crostul
    Nov 29 at 22:22












  • got it, thank you!
    – TBox
    Nov 29 at 22:28










  • @ArseniyBakaev The inequality $e^tge 1+t$ is easily proven: See math.stackexchange.com/q/1330815/215011
    – grand_chat
    Nov 29 at 22:28












  • @Crostul Right, and the justification that $int_0^pi sin^4 (x) dx>0$ will equally apply to $int_0^pi e^{sin^2x}dx > int_0^pi (1+sin^2x)dx$.
    – grand_chat
    Nov 29 at 22:55




















  • I've taken and it equals to $int_0^pi(1+sin^2x)dx = {3over2}pi$ But is it really right to use $e^tge 1+t$?
    – TBox
    Nov 29 at 22:20












  • $$e^t > 1+t$$ is true for all nonzero real numbers, hence it is not necessary to use the second term of Taylor expansion.
    – Crostul
    Nov 29 at 22:22












  • got it, thank you!
    – TBox
    Nov 29 at 22:28










  • @ArseniyBakaev The inequality $e^tge 1+t$ is easily proven: See math.stackexchange.com/q/1330815/215011
    – grand_chat
    Nov 29 at 22:28












  • @Crostul Right, and the justification that $int_0^pi sin^4 (x) dx>0$ will equally apply to $int_0^pi e^{sin^2x}dx > int_0^pi (1+sin^2x)dx$.
    – grand_chat
    Nov 29 at 22:55


















I've taken and it equals to $int_0^pi(1+sin^2x)dx = {3over2}pi$ But is it really right to use $e^tge 1+t$?
– TBox
Nov 29 at 22:20






I've taken and it equals to $int_0^pi(1+sin^2x)dx = {3over2}pi$ But is it really right to use $e^tge 1+t$?
– TBox
Nov 29 at 22:20














$$e^t > 1+t$$ is true for all nonzero real numbers, hence it is not necessary to use the second term of Taylor expansion.
– Crostul
Nov 29 at 22:22






$$e^t > 1+t$$ is true for all nonzero real numbers, hence it is not necessary to use the second term of Taylor expansion.
– Crostul
Nov 29 at 22:22














got it, thank you!
– TBox
Nov 29 at 22:28




got it, thank you!
– TBox
Nov 29 at 22:28












@ArseniyBakaev The inequality $e^tge 1+t$ is easily proven: See math.stackexchange.com/q/1330815/215011
– grand_chat
Nov 29 at 22:28






@ArseniyBakaev The inequality $e^tge 1+t$ is easily proven: See math.stackexchange.com/q/1330815/215011
– grand_chat
Nov 29 at 22:28














@Crostul Right, and the justification that $int_0^pi sin^4 (x) dx>0$ will equally apply to $int_0^pi e^{sin^2x}dx > int_0^pi (1+sin^2x)dx$.
– grand_chat
Nov 29 at 22:55






@Crostul Right, and the justification that $int_0^pi sin^4 (x) dx>0$ will equally apply to $int_0^pi e^{sin^2x}dx > int_0^pi (1+sin^2x)dx$.
– grand_chat
Nov 29 at 22:55












up vote
0
down vote













We can also use Taylor expansion: $e^{sin^2(x)}=1+sin^2(x)+sin^4(x)/2+...$ and integrate it from $0$ to $pi$



$int_0^pi(1+sin^2(x)+(sin^4(x))/2)dx=(27pi)/16 ≈ 5.3014 > 3pi/2$






share|cite|improve this answer























  • Why post this, which copies the idea of a previous answer, only more clumsily?
    – Did
    Dec 5 at 0:06















up vote
0
down vote













We can also use Taylor expansion: $e^{sin^2(x)}=1+sin^2(x)+sin^4(x)/2+...$ and integrate it from $0$ to $pi$



$int_0^pi(1+sin^2(x)+(sin^4(x))/2)dx=(27pi)/16 ≈ 5.3014 > 3pi/2$






share|cite|improve this answer























  • Why post this, which copies the idea of a previous answer, only more clumsily?
    – Did
    Dec 5 at 0:06













up vote
0
down vote










up vote
0
down vote









We can also use Taylor expansion: $e^{sin^2(x)}=1+sin^2(x)+sin^4(x)/2+...$ and integrate it from $0$ to $pi$



$int_0^pi(1+sin^2(x)+(sin^4(x))/2)dx=(27pi)/16 ≈ 5.3014 > 3pi/2$






share|cite|improve this answer














We can also use Taylor expansion: $e^{sin^2(x)}=1+sin^2(x)+sin^4(x)/2+...$ and integrate it from $0$ to $pi$



$int_0^pi(1+sin^2(x)+(sin^4(x))/2)dx=(27pi)/16 ≈ 5.3014 > 3pi/2$







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Dec 4 at 22:45









amWhy

191k28224439




191k28224439










answered Dec 4 at 19:13









TBox

233




233












  • Why post this, which copies the idea of a previous answer, only more clumsily?
    – Did
    Dec 5 at 0:06


















  • Why post this, which copies the idea of a previous answer, only more clumsily?
    – Did
    Dec 5 at 0:06
















Why post this, which copies the idea of a previous answer, only more clumsily?
– Did
Dec 5 at 0:06




Why post this, which copies the idea of a previous answer, only more clumsily?
– Did
Dec 5 at 0:06










up vote
-2
down vote













The integral is a Bessel function:



$$sqrt{e} pi I_0left(frac{1}{2}right)$$



which has numerical value $5.50843$, which is indeed less than $3 pi/2$. This, it would seem, answers the question completely in a principled, and correct manner. One might try any number of other techniques, but I cannot see how any could be better than solving the integral exactly.






share|cite|improve this answer























  • Is it possible to compare without Bessel function?
    – TBox
    Nov 29 at 21:57










  • The only other way to compare would be a numerical integration.
    – David G. Stork
    Nov 29 at 21:58










  • @DavidG.Stork Bessel function does the trick, but in order to just find a soft result, you can go by the ML inequality as elaborated below.
    – Rebellos
    Nov 29 at 22:03










  • "The only other way to compare would be a numerical integration" Not true.
    – Did
    Dec 5 at 0:05















up vote
-2
down vote













The integral is a Bessel function:



$$sqrt{e} pi I_0left(frac{1}{2}right)$$



which has numerical value $5.50843$, which is indeed less than $3 pi/2$. This, it would seem, answers the question completely in a principled, and correct manner. One might try any number of other techniques, but I cannot see how any could be better than solving the integral exactly.






share|cite|improve this answer























  • Is it possible to compare without Bessel function?
    – TBox
    Nov 29 at 21:57










  • The only other way to compare would be a numerical integration.
    – David G. Stork
    Nov 29 at 21:58










  • @DavidG.Stork Bessel function does the trick, but in order to just find a soft result, you can go by the ML inequality as elaborated below.
    – Rebellos
    Nov 29 at 22:03










  • "The only other way to compare would be a numerical integration" Not true.
    – Did
    Dec 5 at 0:05













up vote
-2
down vote










up vote
-2
down vote









The integral is a Bessel function:



$$sqrt{e} pi I_0left(frac{1}{2}right)$$



which has numerical value $5.50843$, which is indeed less than $3 pi/2$. This, it would seem, answers the question completely in a principled, and correct manner. One might try any number of other techniques, but I cannot see how any could be better than solving the integral exactly.






share|cite|improve this answer














The integral is a Bessel function:



$$sqrt{e} pi I_0left(frac{1}{2}right)$$



which has numerical value $5.50843$, which is indeed less than $3 pi/2$. This, it would seem, answers the question completely in a principled, and correct manner. One might try any number of other techniques, but I cannot see how any could be better than solving the integral exactly.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Dec 5 at 0:44

























answered Nov 29 at 21:56









David G. Stork

9,33721232




9,33721232












  • Is it possible to compare without Bessel function?
    – TBox
    Nov 29 at 21:57










  • The only other way to compare would be a numerical integration.
    – David G. Stork
    Nov 29 at 21:58










  • @DavidG.Stork Bessel function does the trick, but in order to just find a soft result, you can go by the ML inequality as elaborated below.
    – Rebellos
    Nov 29 at 22:03










  • "The only other way to compare would be a numerical integration" Not true.
    – Did
    Dec 5 at 0:05


















  • Is it possible to compare without Bessel function?
    – TBox
    Nov 29 at 21:57










  • The only other way to compare would be a numerical integration.
    – David G. Stork
    Nov 29 at 21:58










  • @DavidG.Stork Bessel function does the trick, but in order to just find a soft result, you can go by the ML inequality as elaborated below.
    – Rebellos
    Nov 29 at 22:03










  • "The only other way to compare would be a numerical integration" Not true.
    – Did
    Dec 5 at 0:05
















Is it possible to compare without Bessel function?
– TBox
Nov 29 at 21:57




Is it possible to compare without Bessel function?
– TBox
Nov 29 at 21:57












The only other way to compare would be a numerical integration.
– David G. Stork
Nov 29 at 21:58




The only other way to compare would be a numerical integration.
– David G. Stork
Nov 29 at 21:58












@DavidG.Stork Bessel function does the trick, but in order to just find a soft result, you can go by the ML inequality as elaborated below.
– Rebellos
Nov 29 at 22:03




@DavidG.Stork Bessel function does the trick, but in order to just find a soft result, you can go by the ML inequality as elaborated below.
– Rebellos
Nov 29 at 22:03












"The only other way to compare would be a numerical integration" Not true.
– Did
Dec 5 at 0:05




"The only other way to compare would be a numerical integration" Not true.
– Did
Dec 5 at 0:05



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