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

*To*: mathgroup at smc.vnet.net*Subject*: [mg129890] Re: ComplexExpand off by a factor of (-1)?*From*: Murray Eisenberg <murray at math.umass.edu>*Date*: Sat, 23 Feb 2013 07:01:46 -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*References*: <20130222060524.703B768D0@smc.vnet.net>

Hint: in your expression, replace 2*I by 2*k and you'll see why Mathematica gave you the correct value, i.e., exactly what you asked for! On Feb 22, 2013, 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]? > > Thanks. > > Charles S. --- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2838 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305

**References**:**ComplexExpand off by a factor of (-1)?***From:*charles.ces@gmail.com