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Re: Simplifying trigonometric functions

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  • Subject: [mg94675] Re: [mg94662] Simplifying trigonometric functions
  • From: "David Park" <djmpark at comcast.net>
  • Date: Sat, 20 Dec 2008 06:19:35 -0500 (EST)
  • References: <28161976.1229689867901.JavaMail.root@m02>

Here are two methods. The first is to Map TrigReduce directly to the y
factors.

Cos[x] Cos[y]^2 + Sin[y]^2;
MapAt[TrigReduce, %, {{1, 2}, {2}}]

The second method is to use a rule that operates only on the y factors.

Cos[x] Cos[y]^2 + Sin[y]^2;
% /. (f : (Sin | Cos))[y]^2 :> TrigReduce[f[y]^2]


David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/  



From: Tang [mailto:tangwt at msn.com] 

Hi,
I'm new to Mathematica.
How can I define a rule to reduce the following expression 
from
Cos[x] Cos[y]^2 + Sin[y]^2

to operate only on expressions involving y to

Cos[x](1+Cos[2y])/2 + (1-Cos[2y])/2

Thanks for the help!




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