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Re: Question about trig simplify


You could say it is a feauture; not a bug (at least for me).

Anyway Mathematica offers many opportunities for proper/desired
simplifications/factorizations. It just needs to search a little more.

TrigReduce /@ {-2*Sin[a]*Cos[a], 2*Sin[a]*Cos[a]}
{-Sin[2*a], Sin[2*a]}

Execute the following commands for more information

FrontEndExecute[{HelpBrowserLookup["MainBook","3.3.7"]}]

r = {{Cos[a], Sin[a]}, {-Sin[a], Cos[a]}};

r . r
{{Cos[a]^2 - Sin[a]^2, 2*Cos[a]*Sin[a]}, {-2*Cos[a]*Sin[a], Cos[a]^2 -
Sin[a]^2}}

TrigReduce[%]
{{Cos[2*a], Sin[2*a]}, {-Sin[2*a], Cos[2*a]}}

TrigReduce[r . r . r]
{{Cos[3*a], Sin[3*a]}, {-Sin[3*a], Cos[3*a]}}

Regards
Dimitris


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