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

*To*: mathgroup at smc.vnet.net*Subject*: [mg104450] Re: Answer for Simplify[Cos[x]^4-Sin[x]^4]?*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Sun, 1 Nov 2009 03:57:38 -0500 (EST)

On 10/30/09 at 2:19 AM, lawrenceteo at yahoo.com (Lawrence Teo) 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. When you did the subtraction did you do: In[5]:= Cos[x]^2 - Sin[x]^2 - (Cos[x]^4 - Sin[x]^4) // Simplify Out[5]= 0 which is correct. Or did you fail to include the parentheses and do In[6]:= Cos[x]^2 - Sin[x]^2 - Cos[x]^4 - Sin[x]^4 // Simplify Out[6]= -2 sin^4(x) Since, this result could be characterized as a "small delta", my guess is this is what you did. But this is not the difference between the two expressions.