1
$\begingroup$

Why don't I obtain that $x$ belongs to the Reals?

FunctionDomain[x^2 + 4, x]
(* Out: True *)

FunctionDomain[x^2 + 4, x, Reals]
(* Out: True *)

However, there is no problem here:

FunctionDomain[Log[x]/Sqrt[x + y], x]
(* Out: x > 0 && x + y > 0 *) 
$\endgroup$

closed as off-topic by corey979, MarcoB, m_goldberg, Coolwater, Lukas Lang Jun 27 '18 at 14:52

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question arises due to a simple mistake such as a trivial syntax error, incorrect capitalization, spelling mistake, or other typographical error and is unlikely to help any future visitors, or else it is easily found in the documentation." – corey979, MarcoB, m_goldberg, Coolwater, Lukas Lang
If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ True its mean in this case x \[Element] Interval[{-Infinity, Infinity}]. $\endgroup$ – Mariusz Iwaniuk Jun 21 '18 at 19:18
5
$\begingroup$

FunctionDomain tells you quantitatively what the domain is:

FunctionDomain[Sqrt[x], x]
(* x >= 0 *)

True just means "no limits" here.

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.