Re: ChebyshevT command syntax and polynomial question using

*To*: mathgroup at smc.vnet.net*Subject*: [mg88298] Re: ChebyshevT command syntax and polynomial question using*From*: ratullochjk2 at gmail.com*Date*: Thu, 1 May 2008 03:19:40 -0400 (EDT)*References*: <fv9af1$ms0$1@smc.vnet.net> <fv9ju0$54j$1@smc.vnet.net>

thanks but when I test for x =3 x= 7 21 - 10 x + x^2 I get zero for both answers 1/2 Cos[2 ArcCos[x]] + 43/2 - 10 x also gives me 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 Am I doing something wrong or leaving a part out? tia sal2 On Apr 30, 1:07 am, Szabolcs Horv=E1t <szhor... at gmail.com> wrote: > ratulloch... at gmail.com wrote: > > Greetings All > > > I execute the command and get the following output: > > > In[83] := FunctionExpand[1/2 Cos[2 ArcCos[x]] + 43/2 - 10 x] // Expand= > > Out[83]:= 21 - 10 x + x^2 > > > What would be the proper format to execute the polynomial using > > ChebyshevT to do it in reverse order? > > > Example: > > I would input > > In[83] := FunctionExpand[ChebyshevT[n, x]] > > and it gives me > > Out[83]:= Cos[n ArcCos[x]] > > > How can I do a > > In[83] := FunctionExpand[ChebyshevT[n, x]] > > and it would give me > > Out[83]:= 1/2 Cos[2 ArcCos[x]] + 43/2 - 10 x > > Use TrigReduce: > > 21 - 10 x + x^2 /. x -> Cos[y] // TrigReduce