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Re: Extensive replacement of trigonometric functions

So, you don't want Mathematica to evaluate the expression -Cos[\
[Theta] + (2 \[Pi])/3]?
Since -Cos[\[Theta] + (2 \[Pi])/3] = Sin[\[Theta] + \[Pi]/6], I assume
you want to format the output for visualization purposes, because both
expressions will give the same results. If this is the case, I would
take two approaches: either apply a Hold to the rhs of the rule, or
I'd use a rule of the type Sin[\[Theta]_ + \[Pi]/6] :> -cos[\[Theta] +
(2 \[Pi])/3], so that the inexistent function "cos" keeps unevaluated.
If then you want to evaluate the expression you can release the Hold
or define cos[\[Theta]_] := Cos[\[Theta]].
Hope it helps.

On Feb 17, 6:29 am, Mauro <pi... at> wrote:
> Hello to everybody.
> I have this problem: I would like to replace in a long expression all
> the occurrences of:
> Sin[\[Theta]_ + \[Pi]/6] and Sin[\[Theta]_ - \[Pi]/6]
> with respectively:
> -Cos[\[Theta] + (2 \[Pi])/3] and Cos[\[Theta] - (2 \[Pi])/3]
> (which actually are the same thing).
> Regretfully, the application of the rules:
> Sin[\[Theta]_ + \[Pi]/6] -> -Cos[\[Theta] + (2 \[Pi])/3]
> Sin[\[Theta]_ - \[Pi]/6] -> Cos[\[Theta] - (2 \[Pi])/3]
> results in a flop, since sine functions stubbornly appear again!
> Can you help me?
> Thank you in advance
> Mauro

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