Chapter 1.3, Problem 47ES

Given that $\underset{x\to -\infty }{\lim }f\left(x\right)=0$ and $\underset{x\to +\infty }{\lim }f\left(x\right)=+\infty$ evaluate the limit using an appropriate substitution.

$\underset{x\to 0^{+}}{\lim }f\left(1/x\right)$