Is a discontinuous function divided by a continuous function necessarily a discontinuous function

continuitylimits

I know a continuous function divided by a discontinuous function is not necessarily a discontinous function. e.g. $f(x)=0$ and
$
g(x)=\left\{
\begin{aligned}
1,x\ge 0\\
-1,x<0\\
\end{aligned}
\right.
$
,
we know $f(x)$ is continuous and $g(x)$ is discontinuous, while $f(x)/g(x)\equiv0$ is continuous. In this case, the discontinuity is forcibly suppressed by the ZERO.

However, if a discontinuous function divided by a continuous function, what is the conclusion? I can't find the exception.

Best Answer

Yes. Let $f:\mathbb R\to\mathbb R$ be any function and $g:\mathbb R\to\mathbb R$ be continuous with $g(x)\neq 0$ for all $x\in\mathbb R$ such that $f/g=:h$ is continuous. Then $f=gh$ must be continuous as well, as it is then the product of two continuous functions.

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