Determine the length of the curve sin(x)

[Loren Booda]

What is the measure of the sin(x) wave for x=0 to 2∏?

 

[disregardthat]

It's \int^{2\pi}_0\sqrt{\cos(x)^2+1} dx

 

[Loren Booda]

That's what I got. Would one need a table of integrals to determine its numerical value?

 

[HallsofIvy]

Pretty straight forward, isn't it? Considering the other problems you have posted on here, you should be able to do this.

The length of the graph of y= f(x), from x= a to x= b, is given by
\int_{x=a}^b \sqrt{1+ f'(x)^2}dx
With y= f(x)= sin(x), f'(x)= cos(x) so that becomes
\int_{x=0}^{2\pi} \sqrt{1+ cos^2(x)}dx
However, that looks to me like a version of an elliptical integral which cannot be done in terms of elementary functions.

Hey, no fair posting while I'm typing!

 

[D H]

However, that looks to me like a version of an elliptical integral which cannot be done in terms of elementary functions.

Yep. It's 4√2E(1/2), where E(x) is the complete elliptical integral of the second kind.

 

[mathwonk]

to get a numerical value try numerical integration, simpson's rule? etc...

this is no worse than finding the area under the curve from 0 to 1. i.e. both are approximations.(nobody knows what cos(1) is.)