function is not continuous by showing the limit does not exist.
Recall that if a function f of one variable is differentiable at x_0, it has a derivative at x_0 (via the limit definition of derivative). As one consequence, we know that f is continuous at x_0. This is not necessarily so in the case of a function of two or more variables. Consider the function: f(x,y) = (xy^2) / (x^2 + y^