Find Length of Sine Curve using Calculus

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Discussion Overview

The discussion revolves around finding the length of a sine curve using calculus, specifically focusing on the integral of the form integral(sqrt(cos(x)^2+1), x, 0, a). Participants explore various methods and results related to this integral, including approximations and references to elliptic integrals.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty in evaluating the integral for the length of the sine curve and mentions having derived a result through approximations.
  • Another participant references Wolfram Alpha, indicating that the integral results in an elliptic integral of the second kind, and provides a link to further information.
  • A participant discusses their familiarity with elliptic integrals, noting that they typically arise in contexts such as the time period of a simple pendulum without small angle approximations, and emphasizes that these integrals cannot be solved analytically.
  • There is mention of a method of approximation that reportedly yields better results than standard computational methods, with a request for feedback on whether this approach represents a new result.
  • One participant expresses uncertainty about the novelty of the result and seeks guidance on where to further inquire about their findings.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the derived result is new or established, and there are multiple viewpoints regarding the evaluation of the integral and the use of elliptic integrals.

Contextual Notes

Some participants acknowledge limitations in their understanding of elliptic integrals and the methods used for approximation, indicating a reliance on computational tools and the need for further exploration of the topic.

1994Bhaskar
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I tried to find the length of a sine curve using calculus.I got stuck in the integral of integral(sqrt(cos(x)^2+1), x, 0, a). Limits are from 0 to point a,i.e. length of curve from 0 to any point a.With some approximations I found out the length of sine curve as a result.I have attached the derivation of my result.I tried searching books and internet for this result.But couldn't find like this one.It also seems that this result gives more precise answer.
 

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chiro said:
Hey 1994Bhaskar.

I cheated and used the Wolfram Alpha computational knowledge engine and the answer according to them, was that the answer was in the form of an elliptic integral of the 2nd kind. On wikipedia, it gives you this...

I know elliptic integrals.It comes when you try to find time period of a simple pendulum without taking usual approximation:that angular displacement is very small and that
sin(θ)≈θ in radians.But even elliptical integrals can't be solved analytically.You have to solve it in a calculator/computer or use interpolation formula's to carry out integral approximately.However the method of approximation which I used gives a result which gives better answer compared to a calculator or interpolation.In the end of pdf I have given three checks of that result which I haven't seen anywhere.I have also searched the net extensively.That's why I posted here to ask you guys if it's a new result or not??
 
1994Bhaskar said:
I know elliptic integrals.It comes when you try to find time period of a simple pendulum without taking usual approximation:that angular displacement is very small and that
sin(θ)≈θ in radians.But even elliptical integrals can't be solved analytically.You have to solve it in a calculator/computer or use interpolation formula's to carry out integral approximately.However the method of approximation which I used gives a result which gives better answer compared to a calculator or interpolation.In the end of pdf I have given three checks of that result which I haven't seen anywhere.I have also searched the net extensively.That's why I posted here to ask you guys if it's a new result or not??

I don't know if its a new result or not (hell I didn't know what an elliptic integral was!). Hopefully somebody else can give you a better answer.
 
chiro said:
I don't know if its a new result or not (hell I didn't know what an elliptic integral was!). Hopefully somebody else can give you a better answer.

Thanks for your effort.It means a lot.Can you also suggest where else can I put up my query? Or mail someone?
Any help will be useful.
 

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