I see or hear some variation of this often from mathematics teachers: “The answer to 4+5 is 9.” “So if we’re given (5+3)/2, that means we add five and three, then divide the result by two, and that gives us the answer.”
In regular plain English, answers are coupled with questions. Expressions, though, aren’t questions, not by themselves: They’re expressions. We say that “4+5” and “9” are equivalent expressions because they refer to the same quantities.
There’s a high level discussion to be had about the Axiom of Choice and how it applies to algebraic numbers: Each algebraic number has a “simplest” form,* but an infinite quantity of equivalent forms. But I don’t recall ever hearing the Axiom of Choice being presented to K-12 students (we rarely even discuss algebraic numbers, jumping instead from rational to real numbers).
Instead, we just leave as a standard presumption that, in the absence of any clear instructions to the contrary, the standing question for any expression is: What is its simplest form?
In my opinion, this is a rather significant presumption to leave unstated. How much does this presumption impact student understanding down the road?
One thing I’ve been told by students when I ask them what frustrates them in math class is: When I don’t know what I’m supposed to do. Implying questions instead of making them overt hurts this process.
* There is currently an apparent shift going on as to irrational denominators. Without a calculator, division by a radical is difficult, and so √2/2 was considered “simpler” than 1/√2. Now that everyone has ready access to scientific calculators, 1/√2 seems to be emerging as “simpler”.