Chapter 1 - Limits and Continuity - 1.3 Limits At Infinity; End Behavior Of A Function - Exercises Set 1.3 - Page 80: 48

$\lim_\limits{x\to 0^-}f\left(\dfrac{1}{x}\right)=0$

Let $y=\dfrac{1}{x}$ If $x\to 0$ from the left then $y\to -\infty$ That gives, $\lim_\limits{x\to 0^-}f\left(\dfrac{1}{x}\right)=\lim_\limits{y\to -\infty}f(y)$ Since, according to given $\lim_\limits{y\to -\infty}f(y)=0$ We get, $\lim_\limits{x\to 0^-}f\left(\dfrac{1}{x}\right)=0$