1.A function is a relation between a set of inputs and a set of
permissible outputs with the property that each input is related to
exactly one output.
2.The domain of a function is the set of "input" or argument values for which the function is defined.
3.The range is the set into which all of the output of the function is constrained to fall
4.x,y
5.I think there would be infinite ways to express a function.Because we can always change the symbol used in a function.