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conversion of sin to cos

• To: mathgroup at smc.vnet.net
• Subject: [mg87058] conversion of sin to cos
• From: glenn077 at gmail.com
• Date: Sun, 30 Mar 2008 01:18:07 -0500 (EST)

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.