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MathGroup Archive 1998

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Re: Re: Exact value of Cos[Pi/17]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg14876] Re: [mg14851] Re: Exact value of Cos[Pi/17]
  • From: BobHanlon at aol.com
  • Date: Mon, 23 Nov 1998 10:11:54 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 11/20/98 5:07:48 AM, hay at haystack.demon.co.uk writes:

>Christopher Gorski wrote in message <72tt9f$isg at smc.vnet.net>...
>>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 adelphia.net
>>http://www.contrib.andrew.cmu.edu/~cgorski
>>
>>
>>
>
>Christopher (using InputForm for Output cells)
>
>Cos[Pi/17]
>
>Cos[Pi/17]
>
>FunctionExpand[%]
>
>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])])])]
>

Allan,

FunctionExpand does not do this on my system:

$Version

"Power Macintosh 3.0 (May 6, 1997)"

Cos[Pi/17]

Cos[Pi/17]

FunctionExpand[%]

Cos[Pi/17]


Bob Hanlon


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