# Definition:Continuous Function

## Contents

## Definition

### Continuous Complex Function

As the complex plane is a metric space, the same definition of continuity applies to complex functions as to metric spaces.

### Continuous Real Function

### Continuity at a Point

Let $A \subseteq \R$ be any subset of the real numbers.

Let $f: A \to \R$ be a real function.

Let $x \in A$ be a point of $A$.

Then **$f$ is continuous at $x$** if and only if the limit $\displaystyle \lim_{y \to x} f \left({y}\right)$ exists and:

- $\displaystyle \lim_{y \to x} \ f \left({y}\right) = f \left({x}\right)$

### Continuous Everywhere

Let $f : \R \to \R$ be a real function.

Then $f$ is **everywhere continuous** if and only if $f$ is continuous at every point in $\R$.

### Continuity on a Subset of Domain

Let $A \subseteq \R$ be any subset of the real numbers.

Let $f: A \to \R$ be a real function.

Then **$f$ is continuous on $A$** if and only if $f$ is continuous at every point of $A$.