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Topic: How to prove that cos(10°) is not rational ?
Replies: 5   Last Post: Sep 22, 2007 4:36 PM

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Ben Rudiak-Gould

Posts: 210
Registered: 2/2/05
Re: How to prove that cos(10°) is not
rational ?

Posted: Sep 22, 2007 4:36 PM
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egouello@gmail.com wrote:
> Hello,
> I already know that cos(x) is irrational when 0°<x<90° and x<>60° but
> I don't find the proof on the Web.
> Does someone have a reference for that?


Here's a previous sci.math thread on this subject:

http://groups.google.com/group/sci.math/browse_frm/thread/ebac71b907f1f18c

-- Ben



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