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MapAt complaint

• To: mathgroup at yoda.physics.unc.edu
• Subject: MapAt complaint
• From: Richard Mercer <richard at rmercer.wright.edu>
• Date: Tue, 09 Nov 1993 08:46:06 -0500

Martin McClain writes:

>  I want to go from   expr1 = 1+Sin[a+b]+Sin[a-b]
>  

>  to                  expr2 = 1 + 2 Cos[a] Sin[b].
>  I am looking for an easy one liner.  Any suggestions?

This can be done with

Apart[expr1,Trig->True].

However I agree that dealing with trig manipulations is much more  
difficult in Mma than it needs to be; almost a Black Art. Maybe  
someday I'll do something about that.

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