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, firstname.lastname@example.org 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.
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