Mathematica:How can I acclaim a variable is real in a complex function

  1. Hi,I'm a beginner.
    here's the example:
    f[x_] := E^(I*x)
    Conjugate[f[x]]*f[x]
    I'd like get 1,but it give me a complex function coz it regard x as complex.
    please help me:how to claim x is real?

    by the way,is that necessary to define a letter as a constant.no matter yes or not,how to refer a letter constant to be real or pure imaginary

    Thank you!
     
    Last edited: Feb 17, 2009
  2. jcsd
  3. CRGreathouse

    CRGreathouse 3,682
    Science Advisor
    Homework Helper

    You could do
    Code (Text):
    f[x_]:=Exp[I*Re[x]]
    so it takes only the real part of x (which doesn't change it, of course, when x is real).
     
  4. Thanks for your reply.
    I tried your answer,and it works.

    Well,I have some...eerr...
    what if I'd define the domain for function f[x]?
    I mean that I wanna prescribe x in f[x] must be real or pure imaginary or rational number.How to do that.

    I've a similar question here.How to claim a letter constant to be real or pure imaginary or rational number?

    Waiting for your kindness.
     
    Last edited: Feb 18, 2009
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