Re: Wrong Simplify[] Answer for Simplify[Cos[x]^4-Sin[x]^4]?

*To*: mathgroup at smc.vnet.net*Subject*: [mg104413] Re: Wrong Simplify[] Answer for Simplify[Cos[x]^4-Sin[x]^4]?*From*: David Reiss <dbreiss at gmail.com>*Date*: Sat, 31 Oct 2009 01:49:45 -0500 (EST)*References*: <hce437$r4t$1@smc.vnet.net>

Because (Cos[x]^4 - Sin[x]^4) = (Cos[x]^2 - Sin[x]^2) (Cos[x]^2 + Sin[x]^2) and Cos[x]^2 + Sin[x]^2 = 1 --David On Oct 30, 3:20 am, Lawrence Teo <lawrence... at yahoo.com> wrote: > We know that Simplify[Cos[x]^2-Sin[x]^2] -> Cos[2 x] > But why Simplify[Cos[x]^4-Sin[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.