Re: ComplexExpand off by a factor of (-1)?
- To: mathgroup at smc.vnet.net
- Subject: [mg129889] Re: ComplexExpand off by a factor of (-1)?
- From: Bob Hanlon <hanlonr357 at gmail.com>
- Date: Sat, 23 Feb 2013 07:01:26 -0500 (EST)
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- References: <20130222060524.703B768D0@smc.vnet.net>
expr = (E^(I*y) - E^(-I*y))/2*I;
If you plot your expression it is clear that it is -Sin[y] rather than Sin[y]
Plot[expr, {y, -Pi, Pi}]
ComplexExpand[expr]
-Sin[y]
Term-by-term comparison in power series
Assuming[{Element[n, Integers]},
SeriesCoefficient[expr, {y, 0, n}] ==
SeriesCoefficient[-Sin[y], {y, 0, n}] //
FullSimplify]
True
Bob Hanlon
On Fri, 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.
>
- References:
- ComplexExpand off by a factor of (-1)?
- From: charles.ces@gmail.com
- ComplexExpand off by a factor of (-1)?