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Re: Simplifying trigonometric functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg94729] Re: Simplifying trigonometric functions
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Mon, 22 Dec 2008 05:15:13 -0500 (EST)
  • References: <gig3ph$2k4$1@smc.vnet.net>

Tang wrote:
> 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!
> 
Note that if you just want to check an identity, FullSimplify will often 
(but not always - it only has finite power) do the trick:

(Cos[x] Cos[y]^2 + Sin[y]^2 ==
    Cos[x] (1 + Cos[2 y])/2 + (1 - Cos[2 y])/2
   ) // FullSimplify

True

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


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