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From: Walter Roberson <roberson@hushmail.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: arc length
Date: Wed, 07 Apr 2010 09:49:39 -0500
Organization: The University of Manitoba
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bo wrote:

> How to calculate arc length between 2 different radius?As I only know, 
> the arc length inside circle is r*(theta2-theta1).

In addition to what Roger wrote: note that the integration that he 
suggests is correct in theory, but has the technical problem that closed 
forms for the calculation of arc length are known for only a relatively 
small number of shapes. For example there is a whole branch of calculus 
dealing with integration along ellipses, which there is no closed 
formula for, even though we think of them as being such a minor 
variation of circles.