Re: Exact value of Cos[Pi/17]

*To*: mathgroup at smc.vnet.net*Subject*: [mg14851] Re: Exact value of Cos[Pi/17]*From*: "Allan Hayes" <hay at haystack.demon.co.uk>*Date*: Fri, 20 Nov 1998 02:16:59 -0500*References*: <72tt9f$isg@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

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])])])] ?FunctionExpand "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." Allan