Question: what does it mean when solve returns just the variable itself when solving equation for the variable?

When doing solve(res,x); maple returns back x

Does this means the equation is true for any x?

Also, doing PDEtools:-Solve(res,x) returns nothing.

I was trying to check if my solution is valid for an ode, and I obtained res above is what odetest() gives back, I wanted to find for what could res be zero.

Here is the code


And now 


gives nothing.

So I am a little confused what is going on. does solve result mean the equation is true for any (I think the solution I have is correct, so may be what this means,  but wanted to make sure, as I do not think I've seen this before)  And if so, why then PDEtools:-Solve did not return the same result.

Maple 2020.2, windows 10, Physics 897

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