Combination Theorem for Continuous Functions/Quotient Rule

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Theorem

Real Functions

Let $f$ and $g$ be real functions which are continuous on an open subset $S \subseteq \R$.

$\dfrac f g$ is continuous on $S \setminus \set {x \in S: \map g x = 0}$

that is, on all the points $x$ of $S$ where $\map g x \ne 0$.


Complex Functions

Let $f$ and $g$ be complex functions which are continuous on an open subset $S \subseteq \C$.

$\dfrac f g$ is continuous on $S \setminus \set {z \in S: \map g z = 0}$

that is, on all the points $z$ of $S$ where $\map g z \ne 0$.


Sources