Answer
See below.
Work Step by Step
We calculate function values for $x$ values SMALLER than some $x=a$, with the values of $x$ approaching $a$, but not $a$ itself.
We then observe if the function values approach a number. If they do, we estimate the left limit of the function at $x=a$. If they don't, we conclude that there is no left limit.
Similarly from the right side of $x=a$, we let $x$ assume greater values than $a$, getting closer to $a$. We also observe how the function values behave, in order to estimate a right limit, or to conclude that one does not exist.
If both one-sided limits exist and are equal to the same number $L$, we say that $L$ is the limit of the function at $x=a$.
One disadvantage is that we may not be able to PRECISELY determine the limit (although we can increase precision to however much we want).
