Re: conversion of sin to cos

*To*: mathgroup at smc.vnet.net*Subject*: [mg87075] Re: conversion of sin to cos*From*: Narasimham <mathma18 at hotmail.com>*Date*: Mon, 31 Mar 2008 02:03:31 -0500 (EST)*References*: <fsnbe4$da2$1@smc.vnet.net>

On Mar 30, 11:19 am, glenn... 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. Cos[J Pi] is + or - depending on whether J is respy even/odd . If there are m odd Pis and n even Pis, then J = m alone decides the sign, - for odd m and + for even m. HTH