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ComplexExpand off by a factor of (-1)?

• To: mathgroup at smc.vnet.net
• Subject: [mg129882] ComplexExpand off by a factor of (-1)?
• From: charles.ces at gmail.com
• Date: Fri, 22 Feb 2013 01:05:24 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• Delivered-to: l-mathgroup@wolfram.com
• Delivered-to: mathgroup-newout@smc.vnet.net
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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.

• Follow-Ups:
  • Re: ComplexExpand off by a factor of (-1)?
    • From: Raul Martinez <raulmart@mac.com>
  • Re: ComplexExpand off by a factor of (-1)?
    • From: Murray Eisenberg <murray@math.umass.edu>
  • Re: ComplexExpand off by a factor of (-1)?
    • From: Bob Hanlon <hanlonr357@gmail.com>