# FunctionDomain working with real part

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?

• Looks like a bug. Here's a workaround: FunctionDomain[Re[(I + 1) x] // ComplexExpand, x] – J. M. will be back soon Nov 13 '17 at 5:58
• 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 – Giancarlo Nov 13 '17 at 6:06