Re: ComplexExpand
- To: mathgroup at smc.vnet.net
- Subject: [mg44321] Re: ComplexExpand
- From: Friedrich Laher <mathefritz at schmieder-laher.de>
- Date: Wed, 5 Nov 2003 10:00:52 -0500 (EST)
- References: <bo7osg$aih$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
thank you, folks, I meanwhile know it's a bug(?) in my mathematica 4.2 . Friedrich Laher wrote: > It IS TRUE, for integer n > 0 and real x > that > for s = Sum[Binomial[n,k]Cos[x(n-2k],{k,0,n}] > > s ==(2 Cos[x])^n > but > the only way to verify that by mathematica > seems to be > > (s/.n -> m)/(s/.n -> m-1) > which > results in 2 Cos[x] > > ComplexExpand[s] > > does not know that s is real of value (2 Cos[x])^n > > even if > > s = Simplify[Sum[Binomial[n,k]Cos[x(n-2k],{k,0,n}], > Element[x, Reals] && Element[n,Integers] && n > 0] > > does not know that s is real of value (2 Cos[x])^n > > >