If f(x)=2x the domain of f is all possible values of x for which the function can be evaluated. In this case the domain is the interval (-∞,∞) which can also be written -∞<x<∞. As x→-∞, f(x)→0; as x→∞, f(x)→∞. The curve is continuous between these limits. It passes through (0,1).