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

Posts: 1,647
Registered: 3/14/08
Re: ComplexExpand off by a factor of (-1)?
Posted: Feb 23, 2013 7:01 AM
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On 2/22/13 at 1:05 AM, wrote:

>Would someone be able to help me understand why when I enter the

>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

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