Is there any reason why Mathematica evaluates the following

FunctionDomain[Re[((I + 1) x)], x]
(* False *)

as False, where I'd expect True, since the function is defined for all real x?

  • $\begingroup$ Looks like a bug. Here's a workaround: FunctionDomain[Re[(I + 1) x] // ComplexExpand, x] $\endgroup$ – J. M. will be back soon Nov 13 '17 at 5:58
  • $\begingroup$ Yes, I thought about that, thanks @J.M. It's interesting that FunctionDomain[Re[((I + 0.) x)], x] still gives False while FunctionDomain[Re[( I x)], x] gives True. Also FunctionDomain[Re[((I + 1) x)]^2 + Im[((I + 1) x)]^2, x] gives False while FunctionDomain[Abs[((I + 1) x)]^2, x] gives True $\endgroup$ – Giancarlo Nov 13 '17 at 6:06

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