In computer science, methods (a.k.a. functions) often take more than one input. In the case where a function takes two inputs, we can think of the input (mathematically) as an ordered pair. Consider the following functions from . (Refer back to section 3.6 if you dont recall Cartesian Products.) Is each function one-to-one? Is each onto? If the answer is no, you must provide a specific counterexample.

a. f(x,y)= x^2-y^2

b.f(x,y)=|x|-|y|