Is it true that there is a continuous, onto map from $(0,1]$ to $\mathbb R$?
I am trying but could not approach.
One example is $$ f(x) = \frac{\sin(1/x)}{x} $$
Try $\frac{\sin(\frac{1}{x})}{x}$.
$f(x) = \frac{1}{x}$ maps $(0,1]$ to $[1,+\infty)$. Can you map the latter onto $\Bbb R$ continuously? Then compose.
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One example is $$ f(x) = \frac{\sin(1/x)}{x} $$