How do i do that?
1) x^2 - y = 12
how do i determine whether it defines a function of x?
it depends on how the question was phrased.
it might mean you should solve for y and then say whether what you have is a function, or just note that anything that does not look like "y = something with x's in it" is not defined as a function of x. then there might be cases where you can't solve for y altogether, in which those are definitely not the functions you want