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Re: Exact value of Cos[Pi/17]

  • To: mathgroup at
  • Subject: [mg14871] Re: Exact value of Cos[Pi/17]
  • From: "Allan Hayes" <hay at>
  • Date: Mon, 23 Nov 1998 10:11:51 -0500
  • Sender: owner-wri-mathgroup at

I have received several mails that this is expansion is not working with
Mathematica 3.0x.
Sorry, I find that I was using a beta test copy of the next version.


Allan Hayes
Mathematica Training and Consulting
hay at
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

Allan Hayes wrote in message ...
>Christopher Gorski wrote in message <72tt9f$isg at>...
>>In The Mathematica Book, there is an example on page 936 of Mathematica
>>returning the exact answer to Cos[Pi/17].  When I try it out on my NT
>>machine, however, (mathematica v.3), it simply returns Cos[Pi/17].
>>I've searched throughout the book, and I can't figure out how to get my
>>system to return a answer as in the example given.  It will return
>>simple things, Cos[Pi], for example, returns -1, but more complex
>>arguments won't work.
>>Christopher Gorski
>>cgorski at
>Christopher (using InputForm for Output cells)
>1/4*Sqrt[1/2*(15 + Sqrt[17] + Sqrt[2*(17 - Sqrt[17])] +
>     Sqrt[2*(34 + 6*Sqrt[17] - Sqrt[2*(17 - Sqrt[17])] +
>        Sqrt[34*(17 - Sqrt[17])] -
>        8*Sqrt[2*(17 + Sqrt[17])])])]
>"FunctionExpand[expr] tries to expand out special and certain other
>functions \
>in expr, when possible reducing compound arguments to simpler ones. \
>FunctionExpand[expr, assum] expands using assumptions."

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