Chapter 1 - Limits and Continuity - 1.3 Limits At Infinity; End Behavior Of A Function - Exercises Set 1.3 - Page 80: 47

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

Let $y=\dfrac{1}{x}$ If $x\to 0$ from the right 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 $\lim_\limits{y\to +\infty}f(y)=+\infty$ We get, $\lim_\limits{x\to 0^+}f\left(\dfrac{1}{x}\right)=+\infty$