Re: How Expand?

*To*: mathgroup at smc.vnet.net*Subject*: [mg127845] Re: How Expand?*From*: David Bailey <dave at removedbailey.co.uk>*Date*: Sun, 26 Aug 2012 02:52:23 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net*References*: <k17g9n$dre$1@smc.vnet.net>

On 24/08/2012 10:08, news wrote: > Hi folks, > > How can I expand the following : > > [ 1 + cos(x) + i sin(x) ]^3 > > to obtain; > > 8 cos(x/2)^3 [cos(3x/2)+ i sin(3x/2)] > > Thanks a lot. > > Max. > I addition to the comments of others, I would like to add, that if you simply want to check an identity, it is easier to use: In[9]:= ( 1 + Cos[x] + I Sin[x] )^3==8 Cos[x/2]^3 (Cos[3x/2]+ I Sin[3x/2])//Simplify Out[9]= True (I.e. simplifying the assertion that the LHS == RHS, comes back with True) This works in many situations in which it is extremely hard to force Mathematica to come up with a desired transformation spontaneously. David Bailey http://www.dbaileyconsultancy.co.uk