# Always the same problem with Conjugate [duplicate]

I want to compute something like :

Conjugate[
Sin[θ] (I (2 Sqrt[2] f + h[x]) + Sin[θ] η[x]) Derivative[1][h][x] +
((1 + I) Sqrt[2] f (1 + I Cos[2 θ]) + h[x] Sin[θ]^2 - (Cos[θ]^3 +
I Sin[θ]^3) η[x]) Derivative[1][η][x]] // Refine


I have a list of assumptions requiring that all the quantities (also the derivatives) are Reals so, in principle, Mathematica should be able to replace the I by -I, problem is it does not...

Why is it so difficult for Mathematica to replace the I by -I, I really don't understand because it seems so simple...

Does anyone have a clue why it doesn't work ?

(I also tried Simplify / FullSimplify instead of Refine and it doesn't work as well)

• Have you tried ComplexExpand? – xzczd Apr 9 '14 at 11:54
• What is  Derivative[1] ? – rhermans Apr 9 '14 at 12:02
• The last time I tried ComplexExpand on a more complex expression and it didn't work but on this expression it seems to work so I will retry with ComplexExpand ! Thank you :) – user13568 Apr 9 '14 at 12:04
• @rhermans -> It's the first derivative of h (or \[Eta]) with respect to x – user13568 Apr 9 '14 at 12:06