Re: TrigExpand - Odd behavior

*To*: mathgroup at smc.vnet.net*Subject*: [mg55433] Re: TrigExpand - Odd behavior*From*: DrBob <drbob at bigfoot.com>*Date*: Wed, 23 Mar 2005 05:34:43 -0500 (EST)*References*: <200503220851.DAA23768@smc.vnet.net>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

It's a rather useless result, I agree, but completely accurate (AFAIK). "Degree" is a symbol, so TrigExpand gave you the full expansion (using sum-angle formulas) of the linear expression 45 Degree + x. Try entering Cos[x + 45 y] // TrigExpand (with x and y undefined) and you'll see a similar expression. After the expansion, there were no rules available to simplify its terms. This goes very differently: TrigExpand[Cos[x + Pi/4]] Cos[x]/Sqrt[2] - Sin[x]/Sqrt[2] 45 Degree is Pi/4, but TrigExpand didn't "think" to apply that rule before the expansion. Often mathematics comes down to WHICH rules are used in what ORDER, and TrigExpand is biased toward sum-angle formulas and such. Bobby On Tue, 22 Mar 2005 03:51:07 -0500 (EST), Bob Stagat <stagat at linkline.com> wrote: > > Try executing the following three lines and explain the last result... > > Cos[45 Degree] > > Cos[x+45 Degree] > > Cos[x+45 Degree]//TrigExpand > > Thanks... > ~ BS ~ > > > > -- DrBob at bigfoot.com

**References**:**TrigExpand - Odd behavior***From:*"Bob Stagat" <stagat@linkline.com>