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Re: Transforming a polynomial into a trigonometric format tia sal2

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88241] Re: Transforming a polynomial into a trigonometric format tia sal2
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Tue, 29 Apr 2008 06:50:07 -0400 (EDT)
  • Organization: University of Bergen
  • References: <fv42j9$5ui$1@smc.vnet.net>

ratullochjk2 at gmail.com wrote:
> Transforming a polynomial into a trigonometric format tia sal2
> 
> Greetings All
> 
> I'm using mathematica 6 and I have a polynomial and would like to
> convert it into
> a Trigonometric format.  Is this possible?
> 
> Example:
> I have a polynomial
> 0.00154991- 4.01371 x + 1.81197 x^2 + 8.00183 x^3 - 9.3462 x^4
> 
> How can I transform this into a trigonometric format
> Example:
> 0.00596679 Cos[6.98132 x] + 0.00358397 Cos[7.21403 x] +
>  2.25013 Sin[0.232711 x] - 4.51511 Sin[0.465421 x]
> 
>  Note: these aren't correct answers I just wanted to include and
> example

Hello tia sal2,

I am not sure I understand the question ... Is this what you mean?

In[175]:= poly =
  0.00154991 - 4.01371 x + 1.81197 x^2 + 8.00183 x^3 - 9.3462 x^4

Out[175]= 0.00154991- 4.01371 x + 1.81197 x^2 + 8.00183 x^3 -
  9.3462 x^4

In[176]:= TrigReduce[poly /. x -> Cos[y]]

Out[176]= -2.59729 + 1.98766 Cos[y] - 3.76711 Cos[2 y] +
  2.00046 Cos[3 y] - 1.16828 Cos[4 y]

Szabolcs


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