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MathGroup Archive 1998

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Problem with Expand[Expr, Trig ->True]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg12705] Problem with Expand[Expr, Trig ->True]
  • From: "S. Sankaranarayanan" <sankaras at egr.uri.edu>
  • Date: Wed, 3 Jun 1998 02:20:57 -0400
  • Organization: University of Rhode Island
  • Sender: owner-wri-mathgroup at wolfram.com

Hi

I was trying to use Expand[Expr, Trig ->True] for an  example given in
Mathematica book, second edition. It does not  seem to work.

n[24]:= Expand[Sin[x]^2+Sin[2x]^2]

               2           2
Out[24]= Sin[x]  + Sin[2 x]

Expand[%,Trig ->True]


It gives likes this:
                   2         4         2                             4
             Cos[x]    Cos[x]    Sin[x]            2       2   Sin[x]
Out[25]= 1 - ------- - ------- + ------- + 3 Cos[x]  Sin[x]  - -------
                2         2         2                             2

But it is supposed to give

1    - Cos[2 x] - Cos[4 x]
     -----------------------
                    2
But if I use 

TrigReduce[Sin[x]^2 + Sin[2 x]^2]


It gives the needed answer.

         2 - Cos[2 x] - Cos[4 x]
Out[23]= -----------------------
                    2


Responses will be very much appreciated.

Thanks,

Sankar


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