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[?] Get the imaginary part of an equation?

Daniel Voloshin, BMSTU
Posted 5 years ago

So I have an expression called "y" in the form X+i*Y. I need to get X and Y respectively as separate expressions. Obviously, Re[y]=X and Im[y]=Y. But for some reason functions Re[] and Im[] do not return what I expect. Even though I explicitly defined my variables "a" and "w" as Real numbers. Why is that?

theproblem
POSTED BY: Daniel Voloshin
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You assumed w to be real in the previous input, but Mathematica does not remember that. There are various ways to get what you want:

Im[x + I*y]
ComplexExpand[Im[x + I*y]]
Simplify[Im[x + I*y], Element[x | y, Reals]]
Assuming[Element[x | y, Reals], Refine[Im[x + I*y]]]
$Assumptions = Element[x | y, Reals]
Refine[Im[x + I*y]]
POSTED BY: Gianluca Gorni
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