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Re: How to get the Real and Imaginary part of an expression
Posted:
Jan 5, 2013 2:16 AM


On 1/2/2013 8:14 PM, Eduardo M. A. M. Mendes wrote: > Hello > > I need to extract the real and imaginary part of the following expression > > (w=882)/(s^2+2*z*w*s+w^2) > > where w and z are positive constants. s is a complex variable. > > Applying Re and Im to the expression does not do much. By hand, one can easily find them. >
You can use ComplexExpand.
For example
 expr = s + 2 I b + c ComplexExpand[Re[expr]] (* c + s *)
ComplexExpand[Im[expr]] (* 2 b *) 
For your example, I might do
Clear[s, z, w, a, b]; expr = w/(s^2 + 2*z*w*s + w^2); ComplexExpand[Re[expr /. s > a + I b]]
Nasser



