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Re: Exact value of Cos[Pi/17]

  • To: mathgroup at
  • Subject: [mg21085] Re: Exact value of Cos[Pi/17]
  • From: "Stephen P Luttrell" <luttrell at>
  • Date: Sun, 12 Dec 1999 23:51:53 -0500 (EST)
  • Organization: Defence Evaluation and Research Agency
  • References: <72tt9f$>
  • Sender: owner-wri-mathgroup 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.

In Mathematica 3 the following input:


gives the following output:

(1*(-1)^(1/17))/2 - (1*(-1)^(16/17))/2

Stephen P Luttrell
Signal Processing and Imagery Department
DERA Malvern, St.Andrew's Road
Malvern, United Kingdom, WR14 3PS

+44 (0)1684 894046 (tel)
+44 (0)1684 894384 (fax)
luttrell at (email)

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