A function’s behavior near a point can be characterized by examining sequences that approach that point. Specifically, a function is continuous at a point if, for every sequence of inputs converging to that point, the corresponding sequence of function values converges to the function’s value at that point. Consider the function f(x) = x2. To demonstrate continuity at x = 2 using this approach, one would need to show that for any sequence (xn) converging to 2, the sequence (f(xn)) = (xn2) converges to f(2) = 4. This provides an alternative, yet equivalent, method to the epsilon-delta definition for establishing continuity.
This characterization offers a valuable tool in real analysis, particularly when dealing with spaces where the epsilon-delta definition may be cumbersome to apply directly. It provides a bridge between sequence convergence and function continuity, linking two fundamental concepts in mathematical analysis. Historically, it arose as mathematicians sought to formalize the intuitive notion of a continuous function, contributing to the rigorization of calculus in the 19th century. Its strength lies in its ability to leverage knowledge of sequence convergence to infer information about function behavior.