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Re: conversion of sin to cos

• To: mathgroup at smc.vnet.net
• Subject: [mg87079] Re: conversion of sin to cos
• From: David Bailey <dave at Remove_Thisdbailey.co.uk>
• Date: Mon, 31 Mar 2008 02:04:17 -0500 (EST)
• References: <fsnbe4$da2$1@smc.vnet.net>

glenn077 at gmail.com wrote:
> Hello all,
> 
> Here is my problem. I have a very long product of cosines with
> arguments of the form k*Pi, k being integers.
> I want to convert this expression to a sum of cosines. TrigReduce
> works fine, except that it converts cos to sin.
> So, I want all the sin (after the TrigReduce) to be converted to cos
> and the arguments be of the form p*Pi, p being rational of course.
> It has something to do with Hold or HoldAll, but I don't know the
> details. Or perhaps the TrigReduce can be overridden
> somehow.
> Can someone help?
> Thank's for your time.
> 

It might be helpful to give a small actual example of what you want to 
achieve. As you have described it, I would have thought the answer would 
reduce to +1 or -1.

David Bailey
http://www.dbaileyconsultancy.co.uk