How do i determine if the equation is always, never, or sometimes true

If there is an exception or counterexample whatsoever, then it is sometimes if there is no counterexample, then it is always true.

Always true:holds true no matter what and you cannot think of a counterexample or a theorem proves it like anything times 2 is even
sometimes true; holds true under some circumstances like  anything times 3 is even
Never truer theorem disproves it or there are many counterexamples: negative times negative is negative

Cdoes not have two variables