# Complex number operations: telling Mathematica variables are real

I want to do Conjugate[a + b*I], but when I do that, the solution is Conjugate[a] - I*Conjugate[b]; when for me, a and b are reals.

I want to obtain the following expresion : a-b*I

The same problem exists with the function Abs.

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–  Mr.Wizard Aug 12 '12 at 7:14
–  Artes Aug 12 '12 at 8:32

Conjugate[a + b*I]//ComplexExpand

Refine[Conjugate[a + b*I], {a, b} \[Element] Reals]