technique of $a+\epsilon$ and $a-\epsilon$ to find $\lim_{x\to a^+}$
etc.

e.g., $\lim_{x\to 2^+} \frac{1}{x-2}$ =
 $\lim_{\epsilon \to 0^+} \frac{1}{(2+\epsilon)-2}=1/\epsilon=+\infty$
