Re: ComplexExpand off by a factor of (-1)?

*To*: mathgroup at smc.vnet.net*Subject*: [mg129887] Re: ComplexExpand off by a factor of (-1)?*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Sat, 23 Feb 2013 07:00:46 -0500 (EST)*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

On 2/22/13 at 1:05 AM, charles.ces at gmail.com wrote: >Would someone be able to help me understand why when I enter the >expression: >ComplexExpand[(E^(I*y) - E^(-I*y))/2*I] I get a result of -Sin[y] >instead of Sin[y]? You get -Sin[y] because that is the correct answer. You probably intended In[4]:= ComplexExpand[(E^(I*y) - E^(-I*y))/(2*I)] Out[4]= Sin[y] that is divide by 2 I rather than divide by 2 and *multiply* by I as you did. And since 1/I = -1 you got the correct result