Re: Wrong Simplify[] Answer for

*To*: mathgroup at smc.vnet.net*Subject*: [mg104415] Re: [mg104400] Wrong Simplify[] Answer for*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Sat, 31 Oct 2009 01:50:07 -0500 (EST)*Reply-to*: hanlonr at cox.net

The only difference is numerical noise, i.e., close to the specifed precision. For example, specifying a precision of 200, the difference is less than 10^-198 Chop[Table[(Cos[x]^2 - Sin[x]^2) - (Cos[x]^4 - Sin[x]^4), {x, 0, 7, .001`200}], 10^-198] // Union {0} Bob Hanlon ---- Lawrence Teo <lawrenceteo 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.