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Re: Wrong Simplify[] Answer for Simplify[Cos[x]^4Sin[x]^4]?
 To: mathgroup at smc.vnet.net
 Subject: [mg104407] Re: [mg104400] Wrong Simplify[] Answer for Simplify[Cos[x]^4Sin[x]^4]?
 From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
 Date: Sat, 31 Oct 2009 01:48:38 0500 (EST)
 References: <200910300719.CAA27787@smc.vnet.net>
On 30 Oct 2009, at 16:19, Lawrence Teo wrote:
> We know that Simplify[Cos[x]^2Sin[x]^2] > Cos[2 x]
> But why Simplify[Cos[x]^4Sin[x]^4] > Cos[2 x] too?
>
> Doing subtraction between the two expressions will give small delta.
> This is enough to prove that the two expression shouldn't be the same.
>
> Can anyone give me any insight? Thanks.
>
Easy.
Cos[x]^4Sin[x]^4 == (Cos[x]^2Sin[x]^2])*(Cos[x]^2+Sin[x]^2])
(elementery algebra) ==
Cos[x]^2Sin[x]^2])*1 (elemantary trigonometry)
= Cos[x]^2Sin[x]^2]) = Cos[2x]
Where did you get your "small delta" from? And can you really imagine
that a bug like this would hav esurvived nearly two decades of
Mathematica's existence?
Andrzej Kozlowski
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