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Re: Transforming a polynomial into a trigonometric format tia sal2

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88299] Re: Transforming a polynomial into a trigonometric format tia sal2
  • From: ratullochjk2 at gmail.com
  • Date: Thu, 1 May 2008 03:19:51 -0400 (EDT)
  • References: <fv42j9$5ui$1@smc.vnet.net>

I'm sorry if I didn't explain myself better I hope this clarifies it
better

when I test for x =3 x= 7 for equation:
21 - 10 x + x^2 I get zero for both answers

I used another math program using the ChebyshevT command and I
got this
1/2 Cos[2 ArcCos[x]] + 43/2 - 10 x I tested with x=3 and x=7 and I
also got zero for both

but when I do a TrigReduce

In[148] := 21 - 10 x + x^2 /. x -> Cos[y] // TrigReduce

I get

Out[149]:= 1/2 (43 - 20 Cos[x] + Cos[2 x])
x=3 gives me 31.88
x=7 gives me 14.0293

I would like to use the ChebyshevT in mathematica 6 because I prefer
that software but I'm not sure
how to get the 1/2 Cos[2 ArcCos[x]] + 43/2 - 10 x answer in
mathematica 6

Am I doing something wrong with the TrigReduce function or leaving a
part out why are the answers not even close?

tia sal2

On Apr 27, 10:41 pm, ratulloch... at gmail.com wrote:
> Transforming a polynomial into a trigonometric format tiasal2
>
> 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
>
>  tiasa


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