Checking variable A is determined. (DeterminedQ ?)

Question

How can we (loosely) check whether variable A is determined, not directly computing A?
(= How can we define DeterminedQ function ?)

For example,

In[1] x=a+b
In[2] a=2

Then x is not completely determined yet. So,

In[3] DeterminedQ[x]
Out[3] False

But if we go further

In[4] b=2

then

Out[5] DeterminedQ[x]
Out[5] True

Because now x=4.

I have an idea. My idea is inspecting Definition[x], and get variable names v1,v2,... those constructing x. Then inspect Definition[v1], Definition[v2], ..., repeat, repeat.
If we encounter a variable w such that defition[w] produces Null, then x is not determined, DeterminedQ[x] must be false.
Otherwise, variables at bottom level will turn out to be mixture of determined numbers or strings, etc. In this case DeterminedQ[x] must be true.

But there is a problem in my idea. For example,

b=Sqrt[3+2Sqrt[2]]
x=a*(b-1-Sqrt[2])

Then x is mathematically determined becuase x == a*0 == 0, but according to my idea, DeterminedQ[x] becomes false, because Definition[a] becomes Null.

And if we make a mathematica code,

x = the least even number that is not sum of two prime numbers  

(The code can be written using NestWhile command)
Then the existence of x is not known mathematically, but according to my idea, DeterminedQ[x] becomes true.

I don't care whether x is determined mathematically or not.
I just want DeterminedQ function, which is loose but super fast, always give true or false.

...Or, there may be a built-in function already. Can you construct/know
DeterminedQ-like function ?

Answer 1

How about this?

DeterminedQ[x_List] := And @@ DeterminedQ /@ x;
DeterminedQ[x_] := NumericQ[x];